Unit converter.
Convert length, weight, volume, temperature, area, speed, data and time — instantly.
Metric and imperial, both ways
This converter covers the units that come up most — kilometres and miles, kilograms and pounds, litres and gallons, Celsius and Fahrenheit — across eight categories. Everything is calculated locally as you type, so it's instant and works offline once the page has loaded. A note on the "data" category: it uses binary sizes (1 kilobyte = 1024 bytes), which is how operating systems usually report file sizes. For kitchen-specific measures and ingredient weights, the cooking conversions page is purpose-built; for mental shortcuts, see mental math.
Watch the gallon: US vs imperial
The most common conversion mistake is treating all gallons as equal. A US gallon is 3.785 litres, but an imperial (UK) gallon is 4.546 litres — about 20% larger. So a car rated at 40 miles per US gallon is really doing roughly 48 miles per imperial gallon, even though nothing about the car changed. This converter uses US gallons for volume; pick your unit deliberately when comparing figures from different countries.
It also pays to keep mass and weight separate. A conversion factor is just a ratio equal to one: since 1 kg = 2.2046 lb, multiplying a kilogram value by 2.2046 changes the unit without changing the quantity. To go the other way, divide. Chaining factors works too — 5 km × (1000 m / 1 km) × (1 mi / 1609.34 m) ≈ 3.11 miles.