How the conversions work
Each unit has an exact factor that converts it to a base unit: metres for length, kilograms for weight, litres for volume, square metres for area and metres per second for speed. The converter multiplies your value by the 'from' factor and divides by the 'to' factor.
Temperature is different because the scales start from different points. The converter changes your value to Celsius first: Fahrenheit − 32, × 5 ÷ 9, or Kelvin − 273.15. Then it converts to the scale you want.
Results are shown to up to six decimal places.
Worked examples
100 millimetres × 0.001 ÷ 0.01 = 10 centimetres.
20 °C × 9 ÷ 5 + 32 = 68 °F.
1 imperial gallon is 4.54609 litres, but 1 US gallon is 3.785411784 litres, so check which one you need.
Useful exact factors
1 inch = 2.54 cm, 1 foot = 0.3048 m, 1 mile = 1.609344 km.
1 pound = 0.45359237 kg, 1 stone = 14 pounds = 6.35029318 kg.
1 imperial pint = 0.56826125 litres, 1 acre = 4,046.8564224 square metres, 1 mph = 0.44704 metres per second.
Inputs for the unit converter
What are you converting?
Choose length, weight, volume, area, speed or temperature. The unit lists change to match.
Value
The amount to convert. It must be 0 or more, except for temperature, where negative values are fine down to absolute zero.
From
The unit your value is in. The options depend on what you're converting.
To
The unit you want the answer in. The options depend on what you're converting.
CALCULATOR QUESTIONS
Unit converter questions
How many centimetres are in an inch?
Exactly 2.54 centimetres.
What's the difference between imperial and US gallons?
An imperial gallon is 4.54609 litres and a US gallon is 3.785411784 litres. Imperial pints and fluid ounces are also different from US ones.
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5 and add 32. For example, 20 °C is 68 °F.
How many kilograms are in a stone?
One stone is 14 pounds, which is 6.35029318 kilograms.