Unit converter

One converter for the units of everyday life

Most of the world uses the metric system, but the United States and some other places still use miles, pounds and gallons, and recipes, travel, shopping, engineering and school problems constantly move between the two. A single converter covering the common types saves a search each time: how many kilometres is a marathon in miles, how many kilograms is a person of 12 stone, what is 350 degrees Fahrenheit in Celsius, how many litres are in a gallon of fuel.

Twelve types of unit

• Length: millimetres to kilometres, inches, feet, yards, miles and nautical miles.
• Mass and weight: milligrams to tonnes, ounces, pounds and stone.
• Volume: millilitres and litres, cubic metres, teaspoons, cups, pints, quarts and gallons, both US and UK.
• Area: square units, hectares, acres and square miles.
• Speed, time, pressure, energy and power, including knots, bar, psi, calories, kilowatt-hours, BTU and horsepower.
• Angle: degrees, radians, gradians and full turns.
• Temperature: Celsius, Fahrenheit and kelvin, with the offsets handled correctly.
• Fuel economy: litres per 100 km, kilometres per litre and miles per gallon, with US and UK gallons, which are different sizes.

How the conversion works

For most types each unit is defined as a multiple of a base unit, and converting means multiplying by the ratio of the two. Temperature is different: Celsius, Fahrenheit and kelvin have different zero points as well as different sizes, so an offset is applied. Fuel economy is different again, because litres per 100 km and miles per gallon are inverses of each other: a lower number is better in one and worse in the other. The tool handles those special cases and shows the whole table for the type you choose, so you can see the value in every unit at once.

Know your gallon and your cup

Some units have more than one meaning. A US gallon is 3.785 litres and a UK (imperial) gallon 4.546, which makes a mile per UK gallon about 20% better than the same figure per US gallon. Cups and spoons also differ between countries. The units in this tool that could be ambiguous are labelled with US or UK.

What it does not do

Currency is not included, as it needs live rates. Very large or very small results are shown in scientific notation. For cooking measures by ingredient, from cups to grams, use the cooking converter, and for file sizes the file size converter.