Ask it in words. Get the number, the working, and the source.
Rule Calculator runs fixed formulas, not model arithmetic. Ask in plain English — feet and inches, fractions, mixed units all parse. If no calculator covers your question, one gets built for it on the spot.
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 rectangular, round or triangular area from feet-and-inches measurements, with a waste factor.
- 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 a measurement to feet and inches, or add, subtract, multiply and divide feet-and-inches measurements, with the rounding error printed 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, so a delivery quoted in tons can be checked against a hole measured in yards.
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.
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, or the score you need on the final to reach the grade you want.
- Time CalculatorAdd or subtract two durations in hours, minutes and seconds, with the decimal hours payroll and billing want.
- Grams to Cups ConverterCups to grams and back for real ingredients, because a cup is a volume and flour, sugar and honey do not weigh the same.