How the Unit Converter works

Choose a type (length, weight or volume), enter a value, then pick the unit you are converting from and the unit you want. The result updates as you type. Behind the scenes, every unit is stored as a multiple of one base unit (metres for length, kilograms for weight, litres for volume). Your value is converted to the base unit and then into the target unit in a single calculation, which avoids the rounding errors that build up when you convert in several steps.

Worked examples

10 miles is 16.0934 kilometres. 5 feet is 152.4 centimetres. 150 pounds is 68.0388 kilograms. 2 gallons is 7.5708 litres, and 1 inch is exactly 2.54 centimetres. To go the other way, 70 kilograms is about 154.32 pounds. Results are shown to up to four decimal places, with trailing zeros removed.

Units available

Length covers metres, centimetres, kilometres, inches, feet, yards and miles. Weight covers kilograms, grams, pounds and ounces. Volume covers litres, millilitres, gallons, cups and tablespoons. Weight here means mass as sold in shops and written on labels, so the ounces are weight ounces, not fluid ounces. For fluid ounces and teaspoons, use the Cooking Measurement Converter.

Metric and imperial

Most of the world uses the metric system, while the United States relies mainly on US customary units, and the UK uses a mix of both. That mismatch causes everyday headaches: a sofa listed in inches, a parcel weighed in pounds, or a car’s fuel economy quoted per gallon. A quick conversion takes the guesswork out of buying, shipping, travelling and following instructions written for a different system.

Doing a conversion by hand

Every conversion is a multiplication or division by a fixed ratio. To change miles to kilometres, multiply by 1.60934. To change kilograms to pounds, divide by 0.453592 or multiply by about 2.2046. If you know how many base units are in each unit, the method is always the same: multiply by the starting unit’s size, then divide by the target unit’s size. The calculator does exactly this, so you can use it to check your own working.

Handy mental shortcuts

A kilometre is about six-tenths of a mile, a kilogram is a little over 2.2 pounds, and a litre is a little over a quarter of a US gallon. An inch is about 2.5 centimetres and a foot is about 30 centimetres. These rules of thumb are good for a rough sense of scale, and the converter gives the exact figure when it matters.

A note on gallons and cups

This tool uses US gallons (3.78541 litres) and a metric-style cup of 240 millilitres. UK imperial gallons are larger, at about 4.546 litres, so results will differ if you are working with UK recipes or fuel figures. Always check which gallon or cup a source uses.