How it works
Each unit is defined as a fixed multiple of a base unit (metre, kilogram, square metre, litre or metre per second). To convert, the value is turned into the base unit and then into the unit you want.
Temperature is different, because the scales start from different zero points. It uses an offset as well as a multiple.
The formula
Result = value × (size of from-unit ÷ size of to-unit)
Temperature: °F = °C × 9 ÷ 5 + 32, and K = °C + 273.15.
A worked example
1 acre is 4,046.86 square metres, which is 43,560 square feet. 1 mile is exactly 1.609344 kilometres. 100°C is 212°F.
Frequently asked questions
Why is there no bigha, guntha or katha?
Those land units are not the same everywhere. A bigha or guntha differs by state and sometimes by district, so a single conversion would mislead. Use acres, hectares or square feet, or your local revenue office’s definition.
Which gallon is used?
The US gallon (3.785 litres). The UK gallon is larger, about 4.546 litres, and is not included here.
How much is a quintal?
A quintal is 100 kilograms, and 10 quintals make a tonne. It is widely used for crops in India.
How accurate is it?
The factors are the internationally defined values, and the result is shown to up to eight decimal places.