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Unit Conversion Reference
To convert between units, multiply by the conversion factor: 1 inch = 2.54 cm, 1 pound = 0.4536 kg, 1 US gallon = 3.785 liters, 1 mile = 1.609 km. Temperature is the only category that needs a formula instead of a single factor.
The converter above covers seven categories in one place: length, weight, temperature, volume, area, speed and data storage, in both metric (SI) and US customary units. The factors come from the official definitions published by NIST, most of which have been exact since the international yard and pound agreement of 1959.
The Conversions People Search Most
Exact values unless marked approximate. Divide instead of multiplying to go the other way.
| From | To | Multiply by | Example |
|---|---|---|---|
| inches | centimeters | 2.54 | 12 in = 30.48 cm |
| feet | meters | 0.3048 | 6 ft = 1.8288 m |
| yards | meters | 0.9144 | 100 yd = 91.44 m |
| miles | kilometers | 1.609344 | 26.2 mi = 42.16 km |
| pounds | kilograms | 0.45359237 | 150 lb = 68.04 kg |
| ounces | grams | 28.349523125 | 8 oz = 226.8 g |
| US gallons | liters | 3.785411784 | 15 gal = 56.78 L |
| US fluid ounces | milliliters | 29.5735295625 | 12 fl oz = 354.9 mL |
| US cups | milliliters | 236.5882365 | 2 cups = 473.2 mL |
| square feet | square meters | 0.09290304 | 1,500 sq ft = 139.4 m² |
| acres | square feet | 43,560 | 0.25 ac = 10,890 sq ft |
| mph | km/h | 1.609344 | 65 mph = 104.6 km/h |
| km/h | mph | 0.621371 (approx.) | 100 km/h = 62.1 mph |
Temperature Needs a Formula
Celsius and Fahrenheit start from different zero points, so a single multiplier does not work. Use these instead:
- Celsius to Fahrenheit: °F = °C × 9/5 + 32
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9
- Celsius to Kelvin: K = °C + 273.15
- Fahrenheit to Rankine: °R = °F + 459.67
| Reference point | Celsius | Fahrenheit |
|---|---|---|
| Both scales meet | −40 °C | −40 °F |
| Water freezes | 0 °C | 32 °F |
| Room temperature | 20 °C | 68 °F |
| Body temperature | 37 °C | 98.6 °F |
| Water boils (sea level) | 100 °C | 212 °F |
| Moderate oven | 177 °C | 350 °F |
Quick estimate without a calculator: double the Celsius figure and add 30. At 20 °C that gives 70 °F against an exact 68 °F, close enough for the weather.
US and UK Units With the Same Name
Several units share a name but not a size. Recipes, fuel figures and shipping weights from the UK use the imperial versions.
| Unit | US | UK (imperial) |
|---|---|---|
| Gallon | 3.785 L | 4.546 L |
| Pint | 473 mL | 568 mL |
| Fluid ounce | 29.57 mL | 28.41 mL |
| Ton | 2,000 lb (907 kg, short ton) | 2,240 lb (1,016 kg, long ton) |
A metric ton, sometimes spelled tonne, is 1,000 kg and sits between the two. The US gallon is about 17% smaller than the UK gallon, which is why UK miles per gallon figures look better than US ones for the same car.
Data Storage: 1,000 or 1,024?
Drive makers count in decimal units: 1 GB = 1,000 MB and 1 TB = 1,000,000,000,000 bytes. Windows counts in binary units, where each step is 1,024, but still labels them GB. That is why a new 1 TB drive shows about 931 GB in File Explorer. Nothing is missing; it is the same number of bytes described two ways. The converter above offers both: KB, MB, GB and TB are decimal, while KiB, MiB, GiB and TiB are binary.
How to Convert Any Unit by Hand
- Find the factor from the table above, or look up how many base units one of your units is worth.
- Break mixed units into one unit first. A height of 5 ft 10 in is 70 inches.
- Multiply by the factor. 70 × 2.54 = 177.8 cm.
- Going the other way, divide. 180 cm ÷ 2.54 = 70.9 inches, which is 5 ft 10.9 in.
- Round at the end, not in the middle. Rounding each step compounds the error.