Most-used conversions
| From | To | Multiply by |
|---|---|---|
| Kilometres | Miles | 0.621371 |
| Miles | Kilometres | 1.609344 |
| Kilograms | Pounds | 2.204623 |
| Pounds | Kilograms | 0.453592 |
| Centimetres | Inches | 0.393701 |
| Inches | Centimetres | 2.54 |
| Metres | Feet | 3.280840 |
| Litres | US gallons | 0.264172 |
| Square metres | Square feet | 10.763910 |
| km/h | mph | 0.621371 |
Temperature
Temperature scales have different starting points as well as different step sizes, so you can't just multiply:
Quick estimate: double the Celsius and add 30. 20 °C → about 70 °F (exactly 68).
US and UK measures differ
A US gallon is 3.785 litres, but a UK (imperial) gallon is 4.546 litres, about 20% bigger. Pints differ the same way: a US pint is 473 ml, a UK pint 568 ml. US recipe cups are 236.6 ml. The converter lists both where they differ.
Data: 1000 or 1024?
Storage makers use decimal units: 1 GB = 1,000,000,000 bytes. Many operating systems count in binary units of 1024, which is why a "1 TB" drive shows as about 931 GB on Windows. The binary units have their own names (KiB, MiB, GiB) and the converter includes both.
Metric and imperial at a glance
The metric system builds every unit from powers of ten: 10 millimetres make a centimetre, 100 centimetres a metre, 1,000 metres a kilometre. Imperial and US customary units grew out of everyday measures, so the steps are irregular: 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile, 16 ounces in a pound and 14 pounds in a stone. Since 1959 all of them have been defined exactly in metric terms, which is why these conversions are precise rather than approximate.
Most of the world uses metric for everything. The United States uses customary units day to day, and the UK mixes both: miles and pints alongside kilograms and litres.
Other handy facts
- 1 stone = 14 pounds = 6.35 kg, used for body weight in the UK and Ireland.
- 1 hectare = 10,000 m² ≈ 2.47 acres. A football pitch is about 0.7 ha.
- 1 knot = 1 nautical mile per hour = 1.852 km/h, used at sea and in aviation.
- A year in the converter is 365.25 days, the average including leap years.
Frequently asked questions
How do I convert km to miles?
Multiply kilometres by 0.621371. For example, 10 km is about 6.21 miles.
How do I convert kg to pounds?
Multiply kilograms by 2.20462. For example, 70 kg is about 154.3 lb.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32. For example, 25 °C × 1.8 + 32 = 77 °F.
How many centimetres are in an inch?
Exactly 2.54 centimetres. That is the international definition of the inch.
Why does my 1 TB drive show less space?
Drive makers use 1 TB = 1,000,000,000,000 bytes, but Windows counts in units of 1024, so it shows about 931 GB (GiB).
Last updated October 2026 · More converters