Mathematics & calculation

Choose a 2D shape or 3D solid, enter the dimensions you know and get the area, perimeter, diagonals, angles, surface area and volume.

Find the area of a square from its side (s²) or its diagonal (d² ÷ 2).

Find the distance around a square from its side (4 × s) or its diagonal (2√2 × d).

Multiply length by width to get the area of a rectangle, even with different units for each side.

Find the distance around a rectangle from its length and width: P = 2 × (L + W).

Find the area of a triangle from the base and height, all three sides (Heron's formula) or two sides and the included angle.

Add up the three sides of a triangle, or find the third side with the law of cosines from two sides and the included angle.

Find the area of a circle from its radius, diameter or circumference, in the unit of your choice.

Find the circumference of a circle from its radius or diameter, with the formula C = 2πr explained.

Find the hypotenuse or a missing leg of a right triangle, or check whether a triangle is right-angled with the converse, with a full worked solution.

Find a missing length with the intercept theorem, also called the basic proportionality or side splitter theorem, or test parallel lines with its converse.

Calculate X% of a value, what percentage a value is of a total, the percent change between two values or the original value before a change.

Find a percentage of any value: 20% of 150, 8% sales tax on a price or a 20% tip on a bill.

Find what percentage a value is of a total: 30 out of 150, a test score, a share of your budget.

Find a fourth proportional by cross multiplication, solve inverse proportion, or simplify a ratio.

Find the percentage increase between two values, add X% to a value or work back to the value before the increase.

Find the percentage decrease between two values, reduce a value by X% or work back to the value before the decrease.

Convert length, weight, volume, temperature, pressure, energy, fuel economy, digital storage and electrical units with exact factors.

Convert centimeters to inches and inches to centimeters with the exact factor 1 inch = 2.54 cm, for screens, clothing sizes and product dimensions.

Convert kilograms to pounds (lb) and pounds to kilograms with the exact factor 1 lb = 0.45359237 kg, plus a table of common values.

Convert millimeters to inches and inches to millimeters with the exact factor 1 inch = 25.4 mm, for fasteners, tools, wheels and tires.

Convert degrees Celsius to Fahrenheit and back with the exact formula °F = °C × 1.8 + 32, plus a table of common temperatures.

Convert kilometers to miles and miles to kilometers using the exact factor 1 mi = 1.609344 km, with a table of common values.

Convert meters to feet and feet to meters with the exact factor 1 foot = 0.3048 m, for height, altitude, construction and aviation.

Convert feet to inches and inches to feet with the exact ratio 1 foot = 12 inches, for heights, ceilings and construction dimensions.

Convert ounces (oz) to grams and grams to ounces with the exact factor 1 oz = 28.349523125 g, plus a kitchen-friendly conversion table.

Convert pounds to grams and grams to pounds with the exact factor 1 lb = 453.59237 g, plus a kitchen-friendly conversion table.

Convert liters to US gallons and US gallons to liters with the exact factor 1 US gal = 3.785411784 L, plus a table of common values.

Convert cubic meters to liters and liters to cubic meters with the exact factor 1 m³ = 1,000 L, plus examples for water, pools and tanks.

Convert kilometers per hour to miles per hour and back, using the exact factor 1 mph = 1.609344 km/h, with a table of common speed limits.

Convert square meters to square feet and back with the exact factor 1 ft² = 0.09290304 m², for real estate and home projects.

Convert hectares to acres and acres to hectares with the exact factor 1 acre = 4,046.8564224 m², plus a table of common land areas.

Convert liters to British imperial gallons and UK gallons to liters with the exact factor 1 UK gal = 4.54609 L, plus a table of common values.

Convert pressure from bar to psi and back, using the exact factor 1 bar = 14.5038 psi, with a table of common tyre and equipment pressures.

Convert kilowatts to mechanical horsepower (hp) and metric horsepower (PS) without mixing them up: 1 hp = 745.699872 W, 1 PS = 735.49875 W.

Convert decimal megabytes and gigabytes (MB, GB) to binary mebibytes and gibibytes (MiB, GiB): 1 GB = 1,000,000,000 bytes, 1 GiB = 1,073,741,824 bytes.

Convert yards to meters and meters to yards with the exact factor 1 yard = 0.9144 m, for American football, golf, fabric and swimming pools.

Convert pressure from psi to kilopascals and back with the factor 1 psi = 6.894757 kPa and a table of common pressures.

Convert knots to kilometers per hour and back with the exact factor 1 knot = 1.852 km/h, for sailing, aviation and marine weather.

Convert kilowatt-hours to joules and joules to kWh with the exact factor 1 kWh = 3,600,000 J, plus examples from electricity bills and batteries.

Convert US cups, tablespoons and teaspoons to grams by ingredient: flour, sugar, butter, milk and more.

Draw up to 1,000 random integers or decimals in a range, with or without repeats, for raffles, dice or sampling.

Convert an integer between bases 2 and 36: binary, octal, decimal, hexadecimal or a custom base, with negatives and very large integers.

Write a number in words in English, French, Spanish, German, Italian or Portuguese, or turn written words back into digits.

Add, subtract, multiply, divide and simplify fractions, with every step shown.

Write a euro amount in words for a cheque, or turn a written amount back into figures.

Find the GCF (GCD) and LCM of two or more numbers, with the Euclidean algorithm and prime factorization.

Paste a list of numbers to get its mean, median, mode, range, sum and count.

Calculate the standard deviation and variance of a data set, for a population (σ) and for a sample (s), with the deviations table.