Convert between the most common units instantly.
The Unit Converter handles the most common conversions in one place — length (cm, inches, feet, metres), weight (kg, lbs, stone), temperature (Celsius, Fahrenheit, Kelvin), speed (km/h, mph) and volume. No formulas to remember.
Pick a category — length, weight, temperature, speed, volume or area. Type a value into the "from" box and pick the unit; the equivalent value in the "to" unit updates as you type. Switch direction at any time by swapping the unit pickers; the conversion is symmetric. Several categories support batch conversion — type 5 ft 9 in for height and the metres equivalent appears alongside, or 70 kg and see lbs and stone together. Everything happens locally with no rounding more aggressive than 4 decimal places.
Metric units (metres, kilograms, Celsius) are defined from physical constants and use base-10. Imperial units (feet, pounds, Fahrenheit) come from medieval practical references — a foot was once roughly an actual foot's length. The two systems coexist because the US, Liberia and Myanmar didn't fully transition. Conversions like 1 inch = exactly 2.54 cm and 1 pound = exactly 0.45359237 kg are international agreements signed in the 1959 international yard and pound treaty. Temperature is the odd one out: 0°C = 32°F because Celsius pegs to water freezing while Fahrenheit pegged to a brine solution.
Cooking from a recipe written in different units, working out a holiday luggage weight limit, converting cycling speeds when riding abroad, sizing furniture from imported listings, swapping Fahrenheit oven temperatures to Celsius, or estimating fuel economy across countries.