Why convert units?
Most of the world uses the metric system: metres, kilograms and litres. The United States mainly uses US customary units such as feet, pounds and gallons, and the UK uses a mix, with miles on road signs and pints in pubs. Recipes, DIY plans, travel, science homework and online shopping across borders all mean switching between systems. This converter handles all of them in one place, so you don't have to remember the factors.
What can you convert?
- Length and distance: millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles.
- Weight and mass: milligrams, grams, kilograms, tonnes, ounces, pounds, stone and US and UK tons.
- Volume: millilitres to cubic metres, US teaspoons, tablespoons, cups, pints, quarts and gallons, UK pints and gallons and cubic feet.
- Area: cm², m², ares, hectares, km², square inches, feet and yards, acres and square miles.
- Speed: km/h, m/s, miles per hour, knots and feet per second.
- Temperature: Celsius, Fahrenheit and Kelvin.
Common conversion factors
| From | To | Factor |
|---|---|---|
| 1 inch | centimetres | 2.54 |
| 1 foot | metres | 0.3048 |
| 1 mile | kilometres | 1.609344 |
| 1 pound | kilograms | 0.45359237 |
| 1 ounce | grams | 28.35 |
| 1 US gallon | litres | 3.785 |
| 1 UK gallon | litres | 4.546 |
| 1 acre | square feet | 43,560 |
| 1 hectare | acres | 2.471 |
| 1 knot | km/h | 1.852 |
Since 1959 the inch, foot, yard, mile and pound have been defined exactly in terms of the metre and kilogram, so these conversions are exact.
Examples
- 65 mph to km/h: 65 × 1.609344 ≈ 104.6 km/h. A European limit of 100 km/h is about 62 mph.
- 1 acre to square metres: about 4,047 m², or 43,560 square feet.
- 20 litres to US gallons: 20 / 3.785 ≈ 5.28 gallons.
- 2 metres to feet: 2 / 0.3048 ≈ 6.56 feet, or 6 ft 6.7 in.
Watch out: US or UK
For volume, US and UK units are not the same. A US gallon is 3.785 litres, a UK (imperial) gallon 4.546 litres. A US pint is 473 ml, a UK pint 568 ml. The "ton" differs too: a US short ton is 907 kg, a UK long ton 1,016 kg and a metric tonne 1,000 kg. Always pick the right variant. Recipes from American sites use US measures.
Quick tips
- For height in feet and inches there is cm to inches; for body weight in pounds and stone, kg to lbs.
- For temperature with a chart of oven settings, use Celsius to Fahrenheit.
- To work out the floor area of a room, use the square meter calculator.
Metric prefixes
The metric system is easy to scale because every unit uses the same prefixes: milli means one thousandth, centi one hundredth, deci one tenth and kilo a thousand. So a kilometre is 1,000 metres, a millilitre one thousandth of a litre and a kilogram 1,000 grams. US customary units have no such pattern: there are 12 inches in a foot, 3 feet in a yard and 1,760 yards in a mile, which is why a converter saves so much mental arithmetic. In cooking, 3 teaspoons make a tablespoon and 16 tablespoons make a cup.
Frequently asked questions
How many kilometres are in a mile?
One mile is exactly 1.609344 kilometres. A nautical mile is 1.852 kilometres.
How many litres are in a gallon?
A US gallon is 3.785 litres; a UK (imperial) gallon is 4.546 litres.
How many square feet are in an acre?
43,560 square feet, or about 4,047 square metres.
How do I convert km/h to m/s?
Divide by 3.6. 36 km/h is 10 m/s; 100 km/h is about 27.8 m/s.
How many grams are in an ounce?
A standard (avoirdupois) ounce is 28.35 grams. Precious metals use the troy ounce of 31.1 grams.
Are the conversions exact?
Yes, the calculator uses the official definitions. Results are only rounded for display.
Last reviewed: 2026-10-06. Results are estimates for information only.