Free, open-source calculators that explain every answer

Percentage calculator

Find a percentage of a value or compare one value with another.

Percentage change calculator

Calculate the percentage change from an old value to a new value, with the baseline made explicit.

Fraction calculator

Add, subtract, multiply, divide, or reduce fractions using exact rational arithmetic.

Area calculator

Area of a rectangle, triangle or circle in square metres.

Volume calculator

Volume of a box, cylinder or sphere in cubic metres.

Pythagorean theorem calculator

Find the missing side of a right triangle from the other two.

Unit conversion calculator

Convert supported length, mass, temperature, area, volume, and time units; currency conversion is not included.

Compound interest calculator

See how a one-time deposit grows with compound interest over the years.

Loan payment calculator

Find the monthly payment on a fixed-rate loan and how much of it goes to interest.

Tip splitting calculator

Add a tip to the bill and see what each person pays, to the cent.

Age calculator

Find someone’s age in completed years on any date, with the days lived.

Mean, median and mode calculator

Find the mean, median or mode of a list of numbers and see where each centre falls among your values.

Baker's percentage calculator

Express each dough ingredient as a percentage of flour weight, or find the grams of water, salt or flour from a percentage.

BMI calculator

Calculate adult body mass index from weight and height, with its WHO adult range and the formula.

Resting energy (BMR) calculator

Estimate adult resting energy in kcal/day with the Mifflin–St Jeor equations. A prediction, not a measurement or intake target.

Body fat estimate calculator

Estimate adult body fat percentage from BMI and age with the Deurenberg regression. A rough population estimate, not a measurement.

Calories per serving calculator

Divide a recipe's calories into servings, total them back up, or estimate a weighed portion from the cooked batch.

Circle calculator

Area, circumference or diameter of a circle from its radius.

Concrete slab calculator

Work out how many cubic metres of concrete to order for a rectangular slab, with an allowance.

Confidence interval calculator

Find the margin of error and the interval around a sample mean when σ is known.

Cooking measures converter

Convert cups, spoons, fluid ounces, pints and millilitres for recipes.

Days until calculator

Count the days left until an event, or the days since it passed.

Cups to grams calculator

Convert cups to grams and back using the weight of one cup of your ingredient, such as 120 g for flour.

Cylinder calculator

Volume, total surface or curved surface of a cylinder.

Date difference calculator

Count the days between two dates, with or without both ends included.

Density calculator

Find density from mass and volume, and see how it compares with water.

Discount calculator

Find the sale price after a percentage discount and how much you save, or work out the discount percentage from two prices.

Time duration converter

Convert between milliseconds, seconds, minutes, hours, days and weeks.

Kinetic energy calculator

Find the energy of a moving object from its mass and speed.

Final grade calculator

Find the final exam score you need for a target course grade, or project your grade from an exam score.

Flooring calculator

Work out how many packs of laminate or wood flooring to buy for a room, rounded up to whole packs.

Force calculator

Find the net force from mass and acceleration with Newton’s second law.

Fuel economy calculator

Work out litres per 100 km or kilometres per litre from the distance driven and the fuel used on a trip.

GPA calculator

Find a GPA from quality points and credits, combine terms, or see the points a target GPA needs.

Grade calculator

Turn points into a percent, see what a weighted assessment adds to your course grade, or find the points a target needs.

Weight at a chosen BMI

Find the weight that matches a BMI you choose at your height. It does not claim an ideal personal weight.

Inflation calculator

See what a price will cost in the future, or what future cash is worth today, at a steady inflation rate.

Length converter

Convert between millimetres, centimetres, metres, kilometres, inches, feet, yards and miles.

Board foot calculator

Work out board feet of lumber from actual thickness, width, length and the number of boards.

Macro calculator

Turn your own protein, carbohydrate and fat calorie shares into grams per day with 4/4/9 factors. No split is recommended.

Margin and markup calculator

Find the profit margin on a selling price or the markup on cost.

Mass and weight converter

Convert between pounds, ounces, kilograms, grams and milligrams.

Mortgage calculator

Estimate a monthly mortgage payment from home price, down payment and rate, with optional tax, insurance and HOA.

Oven temperature calculator

Convert oven settings between Celsius and Fahrenheit, and lower a conventional setting for a fan oven.

Paint calculator

Work out how many litres of paint to buy from wall area, coats and the coverage on the label.

Power calculator

Find average power in watts from the energy used and the time taken.

Pressure calculator

Find the pressure a force applies when it is spread over an area.

Probability calculator

Find the chance of not A, of A and B, or of A or B from event probabilities.

Random number picker

Pick a whole number between two limits. The same seed always gives the same pick, so a draw can be repeated and checked.

Ratio calculator

Reduce a ratio such as 16 : 9 to a value per one, or scale it to a new size while keeping the same proportion.

Recipe scaling calculator

Scale any ingredient up or down for a new number of servings, find the scale factor, or work back to the original amount.

Rectangle calculator

Area, perimeter or diagonal of a rectangle from its width and height.

Retirement savings calculator

Project how current savings and yearly contributions could grow by retirement.

ROI calculator

Work out the return on an investment after fees, as a profit and a percentage.

Roof area calculator

Turn a roof footprint and pitch into sloped roof area for ordering shingles, tiles or sheets.

Salary to hourly calculator

Convert an annual salary to hourly pay and back, with weekly and monthly equivalents.

Savings calculator

Project a savings balance from a starting amount, monthly deposits and an interest rate.

Scientific functions calculator

Calculate square roots, whole-number powers, natural logarithms and the sine of an angle in degrees, to ten decimal places.

Speed calculator

Find average speed from the distance travelled and the time it took.

Speed converter

Convert between km/h, mph, metres per second, feet per second and knots.

Sphere calculator

Volume, surface area or diameter of a sphere from its radius.

Standard deviation calculator

Measure how spread out a list of numbers is, as a population or a sample, with the mean and variance shown.

Daily energy (TDEE) calculator

Multiply resting energy by a whole-day factor you choose to explore daily expenditure. No diet target is inferred.

Temperature converter

Convert readings between Celsius, Fahrenheit and Kelvin.

Test score calculator

Turn correct answers into a percent, count questions missed, or find how many you need to pass.

Tile calculator

Work out how many tiles to buy for a floor or wall from the area and tile size.

Time zone converter

Convert a local time between two UTC offsets, including the day change.

Triangle calculator

Area, perimeter or height of any triangle.

Water intake calculator

Turn body weight and a millilitres-per-kilogram factor you choose into litres per day. Not a prescribed drinking target.

Weighted average calculator

Average values that count unequally, such as graded coursework.

Work hours calculator

Turn a shift’s start, end and unpaid break into paid decimal hours.