How to use the unit converter
- Choose a category: length, weight, volume or temperature. The unit menus refill with matching units.
- Enter the value you want to convert. Decimals and negative numbers are fine (negative numbers only make sense for temperature).
- Pick the From and To units, or press Swap units to reverse them, then press Convert.
The result shows up to seven significant digits, plus a “1 unit =” line so you can reuse the factor in your own maths.
Rules of thumb: a meter is a little over 3 feet 3 inches, a kilogram is about 2.2 pounds, a liter is slightly more than a US quart, and a kilometer is about 0.62 miles. They're handy for checking that an answer is in the right ballpark before you rely on it. For kitchen measurements of dry ingredients by weight, use the cups to grams converter, because a cup of flour and a cup of sugar weigh very different amounts.
How it's calculated
Length, weight and volume are converted through one base unit: the meter, kilogram or liter. The value is multiplied by the “from” factor and divided by the “to” factor.
| Unit | Exact factor |
|---|---|
| 1 inch | 0.0254 m |
| 1 foot | 0.3048 m |
| 1 mile | 1,609.344 m |
| 1 pound | 0.45359237 kg |
| 1 ounce | 28.349523125 g |
| 1 US gallon | 3.785411784 L |
| 1 US cup | 236.5882365 mL |
Temperature scales have different zero points, so they use offset formulas instead of a single factor: °F = °C × 9/5 + 32, and K = °C + 273.15. Values below absolute zero (−273.15 °C) are rejected.
Worked example
Miles to kilometers: 5 mi × 1,609.344 ÷ 1,000 = 8.04672 km, a 5-mile run expressed as a distance in kilometers.
Pounds to kilograms: 10 lb × 0.45359237 = 4.535924 kg.
Fahrenheit to Celsius: (100 − 32) × 5/9 = 37.78 °C, a hot summer afternoon.
FAQ
How many centimeters are in an inch?
Exactly 2.54 centimeters. The inch has been defined as 25.4 millimeters since 1959.
Are US and UK gallons the same?
No. A US gallon is 3.785 liters and an imperial (UK) gallon is about 4.546 liters. This converter uses US customary volume units.
How do I convert Fahrenheit to Celsius in my head?
Subtract 30 and halve the result for a rough answer. For the exact value, subtract 32 and multiply by 5/9.
Why does the converter treat weight and mass the same?
In everyday use, pounds, ounces, grams and kilograms are all used for mass, and on Earth they convert with fixed factors. The tool uses those standard factors.