937 calculators, conversions and calendars — every one shows its working.
Ask in plain English — feet and inches, fractions, mixed units all parse. Rule Calculator runs fixed formulas, not model arithmetic, so every answer arrives with its derivation and the standard it comes from. If no calculator covers your question, one gets built for it on the spot.
Everything on the site
Or start from a jobConstruction & Home17Concrete, decking, drywall, roofing, gravel, studsFinance15Mortgages, loans, interest, tax, affordabilityHealth & Nutrition13BMI, calories, macros, pregnancy dates, heart rateMaths & Everyday29Percentages, fractions, areas, time, temperatureConversions418Exact factors from the defining standard, both directionsDates280Days between, days from, business days, days untilCalendars1122024 to 2031, ISO weeks, and the rule behind every holidayNumber bases21Binary, hex, octal, text and Roman numeralsCharts20Read a value off a table instead of typing oneGuides9How to measure the thing before you calculate itPrintables3Rulers and gauges that print at true scale
Calculators
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.
- 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.
- 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.
- 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.
- 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.
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.
- Hourly to Salary CalculatorAnnual, monthly and per-paycheck pay from an hourly rate — and the reverse, an hourly equivalent from a salary.
- 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.
Health & Nutrition
- 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.
- 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.
- 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.
- Milligrams to Millilitres CalculatorVolume of a liquid that holds a given mass, from the concentration on the label — because milligrams and millilitres only relate through that number.
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 millimetre equivalent.
- Height ConverterConverts height between centimetres, metres and feet-and-inches in either direction.
- 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 litres — 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, centimetres and points — and the resolution is the whole question.