Unit converter

Pick a category, type a value (or a calculation): the result appears at once, with the conversion into every unit. Print a conversion table, keep your favourite conversions.

What the tool does

15 categories: length, weight, volume (including cups and spoons), temperature, area, speed, time, pressure, energy, power, data (kB and KiB), fuel economy (L/100 km, mpg), angle, frequency, shoe sizes.
Calculations in the field: type 3*12.5 or (180-32)/1.8; both fields are editable.
Every unit of a category at once, and a conversion table (1 to 20 miles in kilometres, for example) to print or export as CSV.

Frequently asked questions

kB or KiB?

A kilobyte (kB) is 1,000 bytes; a kibibyte (KiB) is 1,024. Drive makers count in GB, operating systems often in GiB: a 1 TB drive shows about 931 GiB.

Are shoe sizes exact?

They are average equivalents and vary between brands. Measure your foot from heel to longest toe and check the brand's guide.

Why isn't fuel economy a simple multiplication?

Litres per 100 km measure fuel per distance, miles per gallon distance per fuel: one is the inverse of the other.

How to use it

Pick a category: length, mass, volume, temperature, area, speed, time, pressure, energy, power, data, fuel economy, angle, frequency or shoe sizes.
Type a value in either field: conversion works both ways. You can type a calculation, for example 5*12+11 inches for 5 ft 11 in (71 in = 180.34 cm).
Set the precision (number of digits) and save your frequent conversions as favourites.
Show “all units” to see the value in every unit of the category, or build a conversion table (from 1 to 100, say) to print or export as CSV.

Handy conversions

Temperature: °C = (°F − 32) × 5/9. 100 °F = 37.78 °C; 0 °C = 32 °F; −40 °C = −40 °F. For a temperature difference, 1 °C equals 1.8 °F, without the 32 offset.
Length: 1 inch = 2.54 cm exactly; 1 foot = 30.48 cm; 1 mile = 1.609344 km; 1 nautical mile = 1,852 m.
Volume: a US gallon is 3.785 L, an imperial gallon 4.546 L. A US recipe cup is about 237 mL.
Fuel economy: L/100 km = 235.215 / mpg (US). 30 mpg US = 7.84 L/100 km. The scale is inverted: more mpg means fewer litres.
Data: a drive sold as “1,000 GB” (powers of 10) shows as 931.32 GiB in the system (powers of 2). It is not a fault: they are two different units.
Shoe sizes: EU 42 is about UK 8 and US 9 (men's). Charts vary between brands: try them on if you can.

Common mistakes

Mixing up kW and kWh: kW is power (a rate of energy), kWh is an amount of energy. A 2 kW heater running for 3 hours uses 6 kWh.
Forgetting the square or cube: 1 m² = 10,000 cm², not 100; 1 m³ = 1,000 L.
Using the wrong gallon or pint: US and imperial units differ by about 20%.
Rounding too early in a multi-step calculation: keep full precision and round at the end.

Sources

Factors come from the International System of Units definitions (BIPM) and the 1959 international yard and pound agreement. Shoe sizes follow the usual correspondences and are rounded to the half size.

Guide written and checked by Erwan Hautot · updated 5 November 2026.