2131 calculators, conversions and calendars — every one shows its working.
Ask in plain English. Feet and inches, fractions and mixed units all parse. Every answer is computed by a fixed formula, never by a language model, and arrives with its working and the standard it comes from. No calculator for your question? One gets built on the spot.
What is on the site?
Or start from a jobConstruction & Home30Concrete, decking, drywall, roofing, gravel, studsFinance86Mortgages, loans, interest, tax, affordabilityHealth & Nutrition41BMI, calories, macros, pregnancy dates, heart rateMaths & Everyday103Percentages, fractions, areas, time, temperatureConversions1306Exact factors from the defining standard, both directionsDates383Days between, days from, business days, days untilCalendars1122024 to 2031, ISO weeks, and the rule behind every holidayNumber bases21Binary, hex, octal, text and Roman numeralsCharts37Read a value off a table instead of typing oneGuides9How to measure the thing before you calculate itPrintables3Rulers and gauges that print at true scale
Which calculator do you need?
See allConstruction & Home
- Board Foot CalculatorConvert lumber dimensions to board feet and price out a cut list, including nominal-vs-actual sizing.
- Concrete CalculatorCubic yards of concrete for a slab, round pad, footing, column, wall or stairs, with bag counts and cost.
- Square Footage CalculatorSquare footage of a room, wall, border, gable end, ring or triangle from feet-and-inches measurements, with a waste factor and the cost.
- Paint CalculatorGallons of paint for a room, after subtracting doors and windows and allowing for the number of coats.
- Tile CalculatorHow many tiles and boxes to order for a floor or wall, with the waste factor the layout actually needs.
- Drywall CalculatorSheets of drywall for a room, plus the screws, tape and joint compound to finish it. Screws, tape and compound too, with the ceiling counted separately.
- Stair CalculatorRiser height, tread count, total run and stringer length from a total rise — checked against the code limits.
- Deck Board CalculatorDecking boards, joists and fasteners for a rectangular deck, accounting for the gap between boards.
- Roofing CalculatorRoofing squares and shingle bundles from the building footprint and the roof pitch. Applies the pitch multiplier, so it is roof area, not footprint.
- Gravel & Aggregate CalculatorCubic yards and tons of gravel, sand, limestone or topsoil for an area at a given depth.
- Fence CalculatorPosts, rails, pickets and concrete for a run of fence at a given post spacing. Sections, posts, rails, pickets and the two bags of concrete each post takes.
- Stud CalculatorStuds and plate lumber for a framed wall at 16 or 24 in on centre, including corners and openings.
- Brick CalculatorBricks and mortar for a wall, by brick size — modular, queen, king or utility. Includes the mortar bags and the masonry sand, at about 125 bricks a bag.
- Feet and Inches CalculatorConvert to feet and inches, or add, subtract, multiply and divide feet-and-inches measurements, with the rounding error shown beside the fraction.
- Cubic Yard CalculatorCubic yards for any footprint and depth, with a waste allowance and the weight of the debris if you are hauling it away.
- Mulch CalculatorCubic yards and bags of mulch for a bed, with a waste allowance and a warning when the depth would smother the roots.
- Material Weight CalculatorWhat a volume of gravel, sand, topsoil or mulch weighs, and what a weight takes up, so tons quoted by a supplier can be checked against yards measured on site.
- Siding CalculatorSquares of siding for a house from its wall dimensions, with openings deducted and waste added.
- Insulation CalculatorBags or batts of insulation for an attic or a wall, from the area and the R-value you are aiming at.
- Concrete Block CalculatorBlocks, mortar and fill for a concrete block wall, from its length and height. Blocks, courses, mortar and the concrete it takes to fill the cores.
- Laminate Flooring CalculatorBoxes of laminate, vinyl plank or engineered flooring for a room, with the waste a plank floor actually needs.
- BTU CalculatorThe cooling or heating capacity a room needs, from its size and the things that change the answer — sun, ceiling height, occupants and a kitchen.
- Topsoil CalculatorHow much topsoil a bed or a lawn needs, in cubic yards and in bags, with the weight — the number that decides truck or car boot.
- Asphalt CalculatorTons of hot-mix asphalt for a driveway or lot at a given compacted thickness, with the density the mix is actually sold at.
- Paver CalculatorHow many pavers a patio or walkway needs at a given paver size and joint width, plus the sand and gravel underneath.
- Sod CalculatorRolls and pallets of sod for a lawn, from the area and the roll size the farm cuts, with the waste a shaped lawn actually needs.
- Recessed Light CalculatorHow many recessed lights a room needs and how far apart, from the ceiling height and the light level the room is for.
- Rebar CalculatorBars, total length and weight of reinforcement for a slab at a given grid spacing, with the lap length the code requires.
- Carpet CalculatorSquare yards of carpet from a 12 ft roll, with the seam waste a room wider than the roll actually costs.
- CFM CalculatorCubic feet per minute a room needs, from its volume and how many times an hour the air has to be changed.
Finance
- Mortgage Payment CalculatorMonthly principal-and-interest payment on a fixed-rate mortgage, plus total interest paid over the full term.
- Compound Interest CalculatorFuture value of a starting balance plus monthly contributions, separating what you put in from what the interest earned.
- Loan Payment CalculatorMonthly payment and total interest on any fixed-rate instalment loan — car, personal or student.
- Credit Card Payoff CalculatorHow many months a card balance takes to clear at a fixed monthly payment, and what the interest costs.
- Savings Goal CalculatorThe monthly contribution needed to reach a target by a date, given what you have saved already.
- Salary CalculatorPay converted between every period — hourly, daily, weekly, biweekly, semi-monthly, monthly and annual — with unpaid holidays and days off taken out.
- Tip CalculatorTip and total from a bill, and what each person owes once it is split — including the rounding that makes the split come out even.
- Fuel Cost CalculatorWhat a trip costs in fuel, from its distance, the mileage the vehicle really gets and the pump price — with the cost per mile to compare on.
- Gas Mileage CalculatorMiles per gallon from a tank of fuel and the miles it covered, with the liters-per-100-km figure and the cost per mile it works out to.
- Unit Price CalculatorPrice per unit for two package sizes at once, so the bigger box can be checked rather than assumed — it is the cheaper one about four times in five, not five.
- Sales Tax CalculatorTax and total from a pre-tax price, plus the reverse — the pre-tax price hidden inside a total you already paid.
- ROI CalculatorReturn on investment as a total percentage and as an annualised rate, so holdings of different lengths compare fairly.
- Rent Affordability CalculatorWhat rent your income supports under both the 30% rule and the stricter 28/36 debt-to-income test.
- Pay Raise CalculatorWhat a raise adds per period and per year, and what it is worth after inflation has taken its share.
- Amortization CalculatorFull payment schedule for a loan, with the option to pay biweekly or add extra each month and see what it saves.
- APY CalculatorAnnual percentage yield from a rate and its compounding frequency, and what it earns on a balance in dollars.
- Auto Loan CalculatorCar payment including sales tax, fees, and a trade-in — with the negative equity most calculators quietly leave out.
- Debt-to-Income Ratio CalculatorFront-end and back-end DTI from your monthly debts, plus the largest housing payment that still fits under each lender ceiling.
- Deferred Payment and Bond CalculatorWhat a loan repaid in one lump sum at maturity grows to, or what a known amount due at maturity is worth today.
- Home Affordability CalculatorThe house price your income supports under the 28/36 rule, with property tax, insurance and HOA inside the limit rather than added on top.
- Interest CalculatorWhat a balance grows to under simple and compound interest, with the gap between the two shown as its own figure.
- Payment CalculatorThe monthly payment on a loan, and how much sooner it clears if you pay a different amount instead.
- CD CalculatorWhat a certificate of deposit is worth at maturity, and what breaking it early costs. Includes the early-withdrawal penalty and the after-tax yield.
- Investment CalculatorWhat regular contributions grow to over time, with the inflation-adjusted figure beside the nominal one.
- Present Value CalculatorWhat a future sum, or a stream of payments, is worth today at a given discount rate. Names what the wait costs, as money and as a share of the nominal total.
- Margin and Markup CalculatorMargin and markup from cost and price — the two are not the same number, and the page shows both every time.
- Mileage Reimbursement CalculatorMileage deduction or reimbursement at the IRS standard rates, split across the mid-year rate change.
- Electricity Cost CalculatorWhat an appliance costs to run by the hour, day, month and year, from its wattage and your tariff.
- 401(k) CalculatorWhat a 401(k) grows to, how much of it is the employer match, and whether your contribution rate leaves any of that match unclaimed.
- Home Equity CalculatorHow much equity you have, how much of it a lender will actually let you borrow, and what the payment on it would be.
- Car Lease CalculatorThe monthly lease payment from the price, residual and money factor — and the interest rate that money factor is hiding.
- Refinance CalculatorWhat refinancing saves each month, what it costs to do, and how long you have to stay for it to have been worth it.
- Budget CalculatorThe 50/30/20 split applied to your take-home pay, against what you are actually spending.
- Depreciation CalculatorStraight line, declining balance and sum-of-years depreciation side by side, with the book value each leaves at the end of a year.
- VA Loan CalculatorA VA mortgage payment with the funding fee worked out from the published table — including the jump on a second use that catches people out.
- Rent vs Buy CalculatorWhat renting and buying each cost over the years you plan to stay, counting the money buying ties up as well as the money it spends.
- FHA Loan CalculatorAn FHA payment with both mortgage insurance premiums at the published rates — and whether the annual one ever ends.
- Average Return CalculatorThe compound annual growth rate of an investment, next to the arithmetic average that overstates it.
- Commission CalculatorCommission on a sale with a split, a base salary and an accelerator above quota. Splits out the brokerage share and the effective rate.
- HELOC CalculatorWhat a home equity line of credit costs while you draw on it, and what the payment jumps to on the day the draw period ends.
- Rental Property CalculatorCap rate, cash flow and cash-on-cash return on a rental, counting the three costs that turn a positive spreadsheet negative.
- Pension CalculatorA defined-benefit pension from years of service and final salary, with the age-62 multiplier cliff and the early-retirement reduction both priced.
- Mutual Fund Fee CalculatorWhat an expense ratio actually costs over the life of an investment — not the yearly fee, but the compounding that fee never gets to do.
- Roth IRA CalculatorWhat a Roth IRA grows to, how much of that balance is growth the IRS never taxes, and what the same money would be worth in a taxable account.
- Traditional vs Roth IRA CalculatorWhich IRA leaves you more after tax, comparing the deduction a traditional IRA gives now against the tax-free withdrawal a Roth gives later.
- RMD CalculatorThe required minimum distribution from a traditional IRA or 401(k), using the IRS Uniform Lifetime Table denominator for your age.
- Annuity Payout CalculatorThe monthly income a lump sum pays out over a fixed number of years at a given return, and how much of that income is interest rather than your own capital.
- Retirement CalculatorWhat your savings reach by retirement and how many years they last against the spending you plan, with inflation applied to both sides.
- Mortgage Payoff CalculatorWhen a mortgage clears if you pay extra each month, how many years that cuts off the term, and what the interest saved comes to.
- Student Loan CalculatorWhat a student loan costs to repay, including interest that builds while you are still studying and the salary the payment implies you need.
- Boat Loan CalculatorMonthly payment on a boat loan including sales tax and trade-in, plus the yearly running cost that decides whether the payment is the affordable part.
- Business Loan CalculatorPayment and true cost of a business loan once origination and packaging fees are taken out of the amount that actually lands in the account.
- Inherited IRA RMD CalculatorWhat an inherited IRA must pay out this year, under the life-expectancy method or the ten-year rule, with the deadline the account has to be empty by.
- Estate Tax CalculatorWhether an estate owes federal tax at all, using the 2026 exclusion of $15,000,000 a person, and what the 40% rate costs on anything above it.
- Debt Consolidation CalculatorWhether one loan beats the debts you are carrying now, comparing the blended rate, the monthly payment and the total interest including the origination fee.
- Roth Conversion CalculatorWhat converting a traditional IRA to a Roth costs in tax now, what it is worth at withdrawal, and the retirement tax rate where the two paths break even.
- Backdoor Roth CalculatorWhat a backdoor Roth costs once the pro-rata rule counts every traditional IRA you own, and what rolling the pre-tax money into a 401(k) first saves.
- GDP CalculatorGross domestic product by the expenditure approach, with the share each component contributes, real GDP after the price deflator, and GDP per head.
- Payback Period CalculatorHow long an investment takes to repay its own cost, both undiscounted and with the cost of capital applied — the two answers differ by years on a long project.
- College Cost CalculatorWhat a degree will cost by the time a child starts, what current savings will have grown to, and the monthly contribution that closes the gap between them.
- Rebate or Low APR CalculatorA dealer offers a rebate or a subsidised rate, never both. This compares the two deals over the same term and says which costs less, and by how much.
- VAT CalculatorValue added tax added to a net price or stripped out of a gross one, with the divisor that makes the second case work and the rate for every EU and UK band.
- Simple Interest CalculatorInterest charged on the principal only, with the compound figure beside it so the gap the two produce over the same term is visible rather than assumed.
- Discount CalculatorThe price after a discount, the amount saved, and what a second discount stacked on the first actually comes to — which is never the two rates added together.
- Future Value CalculatorWhat a sum becomes after compounding, with or without regular additions, and how much of the result is the money you put in rather than the return.
- Down Payment CalculatorWhat deposit a purchase needs at a given percentage, what it leaves to borrow, and where the 20% line sits — the point mortgage insurance stops being charged.
- Property Tax CalculatorProperty tax from a home value, with the two things most calculators skip: the assessment ratio, and the exemption that comes off the value rather than the tax.
- Overtime Pay CalculatorTime-and-a-half, double time and the week’s gross, from the regular rate the FLSA actually uses — which folds in a production bonus and is not your base rate.
- Capital Gains Tax CalculatorFederal tax on a sale, with the long-term rate stacked on top of your other income the way the law does it — and the 3.8% surtax most calculators forget.
- No Tax on Tips CalculatorWhat the tip deduction is actually worth: the deduction is capped at $25,000 and saves you your bracket rate on it, not the whole amount.
- No Tax on Overtime CalculatorOnly the half above your regular rate qualifies, and the deduction saves you your bracket rate on it — this works out both, from the hours you actually worked.
- Lottery Tax CalculatorThe advertised jackpot is neither the cash nor the take-home: the lump sum is roughly 48% of it, 24% is withheld, and the real federal rate is 37%.
- AGI CalculatorAdjusted gross income from your income and the adjustments taken before it — the figure a dozen credits and phase-outs are measured against.
- 1099 Tax CalculatorTotal tax on 1099 income — self-employment tax and income tax together — and the quarterly payment that keeps the underpayment penalty away.
- W-4 Withholding CalculatorWhat to put on line 4(c) of a W-4 to land where you want in April — or what to stop withholding if the refund is too big.
- PayPal Fee CalculatorWhat PayPal takes from a payment and what reaches you, on the US rates published 1 September 2026 — plus the amount to invoice to net a target figure.
- CAGR CalculatorCompound annual growth rate from a start, an end and a span — the one rate that would have produced the same result, beside the average that would not.
- Doubling TimeHow long a quantity growing at a fixed rate takes to double, with the Rule of 72 shortcut beside the exact figure and the error between them.
- Effective Annual RateThe effective annual rate a nominal rate becomes once compounding is counted, and the gap that makes two accounts quoting the same rate pay different amounts.
- Price ElasticityPrice elasticity by the midpoint method, with what the price change does to revenue — the figure the elasticity exists to predict.
- Net Worth CalculatorNet worth from what you own and what you owe, split into liquid and illiquid — with the months of expenses the liquid half would actually cover.
- CPM CalculatorCost per thousand impressions, and the two numbers it hides: what a click actually cost and what the campaign returned.
- WACC CalculatorWeighted average cost of capital from the equity and debt in the mix, with the cost of equity derived through CAPM.
- NPS CalculatorNet Promoter Score from the counts of promoters, passives and detractors, with the margin of error the sample size actually allows.
- Freight Class CalculatorFreight density in pounds per cubic foot and the NMFC class band it falls in, which is what an LTL quote is priced from.
- CBM CalculatorCubic meters of a shipment, and the chargeable weight that follows from it — the larger of actual and volumetric, which is what you pay on.
Health & Nutrition
- Pounds and Ounces ConverterA weight in grams or kilograms as pounds and ounces — the two-unit reading a hospital chart and a kitchen scale actually give.
- Stones and Pounds ConverterA body weight in kilograms as stones and pounds, the way a British scale reads it — with the remainder shown rather than folded into a decimal.
- BMI CalculatorBody mass index from height and weight in either metric or US units, with the CDC category cut-offs.
- TDEE CalculatorHow many calories you burn in a day, from the Mifflin-St Jeor equation and an activity multiplier, with cut and bulk targets beside it.
- Body Fat CalculatorBody fat percentage from tape measurements using the US Navy circumference method, plus lean mass.
- Macro CalculatorGrams of protein, carbohydrate and fat from a calorie target and a diet split. With protein per kilogram, the number a split is judged on.
- Ideal Weight CalculatorReference weight from height by four standard clinical formulas, and the BMI-healthy range they sit inside.
- Water Intake CalculatorDaily fluid target from body weight and exercise, against the NASEM total-water reference intakes.
- Heart Rate Zone CalculatorMaximum heart rate and training zones from age and resting pulse, using Tanaka and the Karvonen reserve method.
- Calories Burned CalculatorEnergy burned by an activity from its MET value, body weight and duration. Net of what you would have burned sitting still, which trackers leave in.
- Due Date CalculatorEstimated due date from a last menstrual period or a known conception date, with the current gestational age.
- Ovulation CalculatorOvulation day and the six-day fertile window from your last period, counted back from the next period rather than forward from day 14.
- Calorie Needs CalculatorDaily calorie target for a weight goal, and the number it becomes after the first five, ten and fifteen pounds come off.
- Weight Loss Timeline CalculatorThe date you reach a goal weight at a given intake, with the deceleration the flat 3,500-calorie rule leaves out.
- BMR CalculatorBasal metabolic rate from the Mifflin-St Jeor, revised Harris-Benedict and Katch-McArdle equations at once, with the disagreement between them shown.
- Protein CalculatorDaily protein from body weight, with the floor the DRI sets and the higher range the training literature uses, kept apart.
- Body Surface Area CalculatorBody surface area by the Mosteller and Du Bois formulas, the measure chemotherapy and paediatric doses are scaled by.
- Body Shape CalculatorBody shape from bust, waist and hips, with the waist-to-hip and waist-to-height ratios the WHO uses to judge risk.
- GFR CalculatorEstimated glomerular filtration rate by the 2021 CKD-EPI equation — the race-free one — with the CKD stage it falls in.
- One Rep Max CalculatorYour one-rep max from a set to failure, by all four published formulas at once, with the spread between them and how far they run high.
- Period CalculatorYour next six periods from the last one, with the prediction window widening the further out it goes — because cycle length varies month to month.
- Pregnancy Weight Gain CalculatorWhere your weight should be at this point in pregnancy, from the 2009 Institute of Medicine ranges for your pre-pregnancy BMI.
- Sleep CalculatorWhat time to go to bed to wake at the end of a sleep cycle rather than in the middle of one, counted back from the alarm you have already set.
- Army Body Fat CalculatorThe Army’s waist-to-height assessment that replaced the tape test in July 2026, with the waist measurement the 0.55 standard allows at your height.
- Conception Date CalculatorWhen conception most likely happened, worked back from a due date or a last period, with the window either side that the single date hides.
- Fat Intake CalculatorHow many grams of fat a day your calorie intake allows, inside the 20-35% range the Dietary Guidelines set, with the saturated fat ceiling separately.
- Lean Body Mass CalculatorLean mass by the Boer, James and Hume equations side by side, with the fat mass each implies — the three disagree by kilograms, so the formula is the answer.
- Target Heart Rate CalculatorTraining zones by Karvonen, which uses your resting heart rate, beside the plain percentage-of-maximum method — the two differ by nineteen beats at 70%.
- Steps to Miles CalculatorSteps to miles and kilometres from a stride derived from your height, not the flat 2,000-a-mile pedometers assume — plus what the walk cost in calories.
- Dog Chocolate ToxicityTheobromine dose a dog has taken from the type and weight of chocolate eaten, against the published thresholds where signs begin and where they turn serious.
- Dog Calorie CalculatorDaily calories a dog needs, from the resting energy requirement formula vets use — 70 x weight^0.75 — multiplied by the factor for its life stage.
- Puppy WeightAdult weight from a puppy's weight and age, on growth curves that differ by breed size — small dogs finish at eight months, giant breeds at eighteen.
- Dog Pregnancy CalculatorWhelping date from the mating date, on the 63-day canine gestation, with the dates each check and each stage of the pregnancy falls due.
- A1C CalculatorA1C converted to estimated average glucose in both units, by the ADAG regression, with the wide individual scatter that regression hides.
- LDL CalculatorLDL cholesterol calculated from a lipid panel by both Friedewald and the Martin-Hopkins method, which disagree most where it matters.
- VO2 Max CalculatorVO2 max from a Cooper 12-minute run or from resting and maximum heart rate, with what each method can and cannot see.
- FFMI CalculatorFat-free mass index from weight, height and body fat, with the height-normalised version and the threshold the original study drew.
- Corrected CalciumSerum calcium adjusted for albumin by the Payne formula, in both conventional and SI units, with the case where the adjustment misleads.
- ANC CalculatorAbsolute neutrophil count from a white cell count and the differential, with the severity bands and the bands that only count segs.
- Milligrams to Milliliters CalculatorVolume of a liquid that holds a given mass, from the concentration on the label — because milligrams and milliliters only relate through that number.
- Air Fryer ConversionConverts an oven temperature and time to air fryer settings — 25 °F cooler and about a fifth less time — and gives the point to start checking.
Conversion & Math
- Percentage Change CalculatorPercentage increase or decrease between two values, with the absolute difference and the multiplier.
- Diagonal & Rafter Length CalculatorHypotenuse of a right triangle in feet and inches — brace lengths, rafter runs, and squaring a layout.
- Percentage CalculatorWhat X% of a number is, plus the discounted price, the marked-up price and the remainder.
- Fraction to Decimal CalculatorConverts fractions to decimals and back, to the nearest 16th, 32nd and 64th, with the millimeter equivalent.
- GCF and LCM CalculatorGreatest common factor and least common multiple of two or three numbers, with the prime factors and the check that ties them together.
- Quadratic Formula CalculatorBoth roots of ax² + bx + c = 0 from the quadratic formula, with the discriminant that says in advance how many real roots there are.
- Military Time ConverterA clock time as military time, with the full chart of all twenty-four hours and the two readings people get wrong: midnight and noon.
- Tire Size CalculatorWhat a tire size means in inches, and what changing it does to the rolling diameter and to the speedometer reading.
- Height ConverterConverts height between centimeters, meters and feet-and-inches in either direction. With the centimeters-to-feet chart most people are actually looking for.
- Circle CalculatorArea, circumference and radius of a circle from its diameter — in square feet and square inches.
- Tank & Cylinder Volume CalculatorVolume of a cylinder in cubic feet, US gallons and liters — round tanks, pools, culverts and post holes.
- Speed & Pace CalculatorAverage speed and running pace from a distance and a time, in both imperial and metric.
- Slope & Grade CalculatorGrade percentage, angle in degrees, ratio and roof pitch from a rise and a run.
- Temperature ConverterConverts between Celsius, Fahrenheit and Kelvin in any direction, with the reference points to sanity-check it.
- Age CalculatorExact age in years, months and days from a birth date, plus the total days lived and the next birthday.
- Fraction CalculatorAdd, subtract, multiply or divide fractions and mixed numbers, with an exact reduced answer and every step shown.
- Simplify Fractions CalculatorReduce a fraction to lowest terms, showing the greatest common divisor it was divided by.
- Mixed Numbers CalculatorConvert a mixed number to an improper fraction and back, and add, subtract, multiply or divide two of them.
- Hours CalculatorHours worked between two times, less breaks, in decimal payroll hours — with what the federal rounding rules do to the total.
- Z-Score to P-Value CalculatorExact p-value from a z-score, one-tailed or two-tailed, with the percentile the score sits at.
- Date CalculatorWhat date falls a given number of days or weeks from another date, counting calendar days or business days.
- Grade CalculatorYour weighted course grade from up to eight categories, by percentage or by points, or the score you need on the final to reach the grade you want.
- Time CalculatorAdd, subtract, multiply or divide durations in days, hours, minutes and seconds, with the decimal hours payroll and billing want.
- Grams to Cups ConverterCups to grams and back for 93 ingredients, and what the same cup weighs depending on how it was filled.
- Cone Volume CalculatorVolume of a cone from its diameter and height, in cubic feet, cubic inches and gallons, with the radius and the base area shown separately.
- Sphere Volume CalculatorVolume and surface area of a sphere from its diameter, in cubic feet, cubic inches and gallons, with the radius shown as its own step.
- Circumference CalculatorCircumference of a circle from its diameter or the other way round, with the radius, the area and the arc of one degree shown alongside.
- Right Triangle CalculatorHypotenuse, area, perimeter and both acute angles of a right triangle from its two legs, with the Pythagorean step shown before the square root.
- Arc Length and Sector Area CalculatorArc length, sector area, chord and sector perimeter from a radius and an angle, with the fraction of the full circle shown as its own step.
- Special Right Triangle CalculatorThe 45-45-90 and 30-60-90 triangles from one known side, with every other side given as an exact multiple rather than a decimal that hides the ratio.
- Semicircle CalculatorArea and perimeter of a half circle from its diameter — and the perimeter is the part people get wrong, because it includes the straight edge.
- Pyramid Volume CalculatorVolume of a rectangular pyramid from its base and height, in cubic feet and cubic yards, with the box of the same base and height shown for comparison.
- Pixels to Inches CalculatorPhysical size of a pixel measurement at a given resolution, in inches, centimeters and points — and the resolution is the whole question.
- Percent Off CalculatorThe sale price after a discount, after a second discount stacked on it, and after tax — with what you actually saved.
- Ratio CalculatorReduce a ratio to simplest terms, restate it as 1 : n, and solve a proportion for its missing term.
- Volume CalculatorVolume of a tank, cube, cylinder, sphere, cone, frustum, pyramid, capsule, ellipsoid or pipe — in cubic feet, US gallons and liters.
- Area CalculatorArea of a rectangle, triangle, circle, sector, ellipse, trapezoid, parallelogram or regular polygon — in square feet, square yards, acres and square meters.
- Distance Formula CalculatorDistance between two points in the plane or in space, with the midpoint and the slope, and every step of the square root shown.
- Distance Between CoordinatesGreat-circle distance between two latitude and longitude pairs, in miles, kilometers and nautical miles, with the initial bearing.
- Fuel Consumption ConverterMiles per gallon, liters per 100 km and kilometers per liter from any one of them, with the US and imperial gallons kept apart.
- Horsepower and Torque CalculatorHorsepower from torque and engine speed, with the kilowatt and metric PS figures the same engine is sold under elsewhere.
- Ohm's Law CalculatorVoltage, current, resistance and power from any two of them, with the whole set printed rather than the one you asked for.
- Engine Displacement CalculatorEngine capacity from bore, stroke and cylinder count, in cubic centimeters, liters and cubic inches.
- Surface Area CalculatorSurface area of a box, cube, cylinder, sphere, cone, pyramid, capsule or ellipsoid, with the lateral area given separately from the ends.
- Slope CalculatorSlope, intercept, angle and the full line equation from two points, with the perpendicular slope beside it.
- Triangle CalculatorEvery angle, the area, the perimeter and the height of any triangle from its three sides, using the law of cosines.
- Density CalculatorDensity from mass and volume, in kilograms per cubic meter, grams per cubic centimeter and pounds per cubic foot, with what floats and what does not.
- Rounding CalculatorA number rounded every way there is — half up, half to even, down, up and truncated — with the ones that disagree shown together.
- Exponent CalculatorA number raised to any power, including negative and fractional ones, with the root it is equivalent to and the answer in scientific notation.
- Logarithm CalculatorA logarithm in any base, with the natural and base-ten values beside it and the change-of-base step shown.
- Half-Life CalculatorHow much of a substance is left after a given time, from its half-life — with the decay constant and the mean lifetime.
- Confidence Interval CalculatorThe confidence interval around a sample mean, with the margin of error and what the interval does and does not claim.
- Sample Size CalculatorHow many people a survey needs for a given margin of error, with the finite population correction that makes small populations cheaper.
- Probability CalculatorTwo events combined every way — both, either, neither, exactly one — plus the chance of at least one occurrence over many tries.
- Resistor Colour Code CalculatorResistance and tolerance from the bands on a resistor, with the E-series value it is meant to be.
- Heat Index CalculatorWhat the temperature feels like at a given humidity, by the National Weather Service regression, with the risk category it falls in.
- Wind Chill CalculatorWhat the cold feels like once wind is taken into account, by the National Weather Service formula, with the frostbite time it implies.
- Dew Point CalculatorDew point from temperature and humidity by the Magnus formula, with what that dew point actually feels like.
- Scientific Notation ConverterA number in scientific, engineering and plain notation at once, with its order of magnitude and significant figures.
- Percent Error CalculatorPercent error against a known value, with percent difference beside it — they are different questions and get confused constantly.
- Number Sequence CalculatorThe nth term and the running total of an arithmetic or geometric sequence, and whether an infinite geometric one converges.
- Molarity CalculatorMolarity from mass and volume, the mass needed for a target concentration, and the dilution that gets you there.
- Download Time CalculatorHow long a file takes at a given connection speed, with the bits-and-bytes factor of eight that makes everyone’s estimate wrong.
- Pythagorean Theorem CalculatorSolves a² + b² = c² in either direction — the hypotenuse from two legs, or the missing leg from a leg and the hypotenuse — with the squares shown.
- Voltage Drop CalculatorVoltage lost along a copper or aluminium run, as volts and as a percentage, against the 3% the NEC recommends for a branch circuit.
- Golf Handicap CalculatorThe score differential a round produces under the World Handicap System, and the course handicap your index converts to on the tees you are playing.
- Day CounterHow many days lie between two dates, counted as calendar days and again as working days, with the span in weeks, months and years.
- Oven Temperature ConverterAn oven setting in Fahrenheit, Celsius, gas mark and the fan equivalent, with the dial rounding real ovens actually offer.
- Completing the Square CalculatorTurns ax² + bx + c into a(x − h)² + k, giving the vertex, the axis of symmetry and the roots that fall straight out of the completed form.
- Absolute Value CalculatorThe absolute value of a number, and the two solutions an equation of the form |ax + b| = c always has — which is the part a bare magnitude does not answer.
- Kinetic Energy CalculatorKinetic energy from mass and speed, with the stopping distance it implies — because the square on the velocity is the part that surprises people.
- Minutes to DecimalHours and minutes as the decimal a payroll system wants, with the quarter-hour rounding the FLSA allows and what it costs you over a year.
- Watts to AmpsWatts to amps and back, with the power factor and the phase that AC needs. A DC answer applied to a 3-phase motor is out by 73%.
- kW and kVA to AmpsCurrent drawn by a load rated in kW or kVA, on any voltage and phase. The unit on the nameplate decides whether power factor enters the sum.
- Volts to WattsVolts alone do not give watts — one more quantity is required. Enter amps, ohms or the wattage and this gives the rest of the set.
- mAh to WhBattery capacity in mAh converted to watt-hours, which is the only figure two batteries at different voltages can be compared on — and the one airlines limit.
- Watts to kWhWatts is a rate and kWh is an amount, so the conversion needs a duration. This gives the energy, the running cost and what the meter will show.
- Joules to WattsA watt is a joule per second, so the conversion is a division by the time. Works either direction, and in kJ, kWh and calories.
- Parallel ResistorsUp to four resistors in parallel or series, with the current each one takes and the power it has to dissipate — which is what decides the rating.
- LED Resistor CalculatorThe series resistor an LED needs, from supply voltage, forward voltage and current — with the power it must dissipate and which standard value to pick.
- Percent DifferencePercent difference between two values, divided by their mean — beside percent change, which divides by one of them and gives a different answer.
- Difference of Two SquaresFactors a² − b² into (a + b)(a − b), multiplied back out as a check — and the mental shortcut it gives for products either side of a round number.
- Midpoint CalculatorThe midpoint of two points, with the distance, the slope and the perpendicular bisector — what a coordinate-geometry question asks about the same pair.
- Dot and Cross ProductDot product, cross product, magnitudes and the angle between two 3-D vectors. The dot returns a number, the cross returns a vector — that is the difficulty.
- Sig Fig CalculatorHow many significant figures a number has and what it rounds to, with the leading, trailing and captive zeros counted by the rules that decide them.
- Correlation CalculatorPearson correlation from the sums a class is given, with r², the slope it implies, and the sample size at which it stops being noise.
- Linear Regression CalculatorThe least-squares line through a set of points, with its slope, intercept, r² and the standard error the prediction carries.
- Binomial CalculatorThe probability of exactly k successes in n independent trials, with the cumulative tails, the mean and the standard deviation.
- Interpolation CalculatorThe value between two known points on a straight line, with the slope it assumes and a warning when the target sits outside them.
- Hypergeometric CalculatorThe probability of drawing exactly k of a kind from a finite population without replacement — the card and lottery case the binomial gets wrong.
- Sin Cos Tan CalculatorSine, cosine and tangent of an angle in degrees or radians, with the angle also shown in the other unit and the reciprocal functions.
- Inverse Trig CalculatorArcsine, arccosine and arctangent: the angle whose sine, cosine or tangent is the ratio you have, in degrees and radians.
- Law of Sines CalculatorSolves a triangle from one side and two angles: the third angle, the remaining two sides and the area, using a/sin A = b/sin B.
- Law of Cosines CalculatorSolves a triangle from two sides and the angle between them: the third side, the other two angles and the area, using c² = a² + b² − 2ab·cos C.
- Factorial Calculatorn factorial for n up to 170, with the number of digits, the previous factorial and what the figure counts: the orderings of n distinct things.
- dBm to Watts CalculatorConverts dBm to watts and milliwatts, and back — the logarithmic power scale radio, fibre and audio equipment is specified in.
- Decibel CalculatorThe decibel figure for a ratio of two powers or two amplitudes, and the ratio a decibel figure stands for, using 10·log₁₀ and 20·log₁₀.
- Lumens to Lux CalculatorIlluminance in lux from a luminous flux in lumens spread over an area, with the foot-candle equivalent and the area needed for a target level.
- Velocity CalculatorFinal velocity from a starting velocity, a constant acceleration and a time, with the distance covered and the average velocity over the interval.
- Momentum CalculatorMomentum from a mass and a velocity, with the kinetic energy that goes with it and the impulse needed to stop the object in a given time.
- Work CalculatorWork done by a force over a distance, with the angle between them, plus the power if it took a given time and the same figure in calories.
- Resonant FrequencyResonant frequency of an LC circuit from inductance and capacitance, with the angular frequency, the period and the capacitance a target frequency needs.
- Mass-Energy CalculatorThe rest energy of a mass from E = mc², in joules, kilowatt-hours and kilotons of TNT, using the defined speed of light.