How to use it
Choose what you want to convert, type the amount and pick the two units. The result updates as you type, and the swap button reverses the conversion. Everything runs in your browser, so it works instantly even with a weak connection.
The conversions people look up most
| US unit | Metric |
|---|---|
| 1 inch | 2.54 cm (exact) |
| 1 foot | 30.48 cm |
| 1 mile | 1.609 km |
| 1 pound | 453.6 g |
| 1 ounce | 28.35 g |
| 1 US gallon | 3.785 liters |
| 1 US cup | 236.6 ml |
| 100 square feet | 9.29 m² |
| 1 acre | 0.405 hectares |
Most of these are exact by definition. The inch, the foot, the yard and the mile have been defined from the meter since 1959, and the pound from the kilogram: 1 lb is exactly 0.45359237 kg.
Why temperature is different
Length or weight conversions are a single multiplication, because zero means the same thing in both units. Temperature scales start at different points, so you have to shift as well as scale:
°C = (°F − 32) × 5 ÷ 9 and °F = °C × 9 ÷ 5 + 32
A comfortable 72 °F room is 22.2 °C. Water freezes at 32 °F (0 °C) and boils at 212 °F (100 °C). Kelvin is Celsius shifted by 273.15, with no degree sign.
US and imperial units aren’t the same
The US and the UK share unit names but not always sizes. An imperial gallon is 4.546 liters, 20% bigger than the US gallon, and the same goes for pints and fluid ounces. The converter lists US and UK gallons separately so you can pick the right one.
Kilobytes: 1,000 or 1,024?
Both are in use. This converter uses 1 KB = 1,024 bytes, the convention Windows uses when it shows file sizes. Drive makers use 1,000, which is why a “1 TB” drive shows up as about 931 GB on a Windows computer: nothing is missing, it’s the same number of bytes counted two ways.
Related tools
If you’re converting to work out a unit price or scale a recipe, the proportion calculator does the rest.