Unit converter
Pick a category, type a value, then choose the units to convert from and to; the answer appears instantly using exact official factors. A few to remember: 1 mile = 1.609344 km, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 US gallon = 3.785411784 liters, and 1 acre = 43,560 sq ft.
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Official conversion factors
Since the 1959 international agreement, US customary units are defined exactly in terms of the meter and kilogram. The factors below are exact, not rounded.
| Unit | Exact value |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 0.3048 m |
| 1 yard | 0.9144 m |
| 1 mile | 1,609.344 m |
| 1 ounce (oz) | 28.349523125 g |
| 1 pound (lb) | 0.45359237 kg |
| 1 US gallon | 3.785411784 L |
| 1 US fluid ounce | 29.5735295625 ml |
| 1 acre | 4,046.8564224 m² (43,560 sq ft) |
How the conversion works
Every unit has a factor relative to a base unit (meter, kilogram, liter). Convert to the base, then divide by the target factor.
\[ \begin{gathered} \text{result} = \dfrac{\text{value} \times \text{factor (from)}}{\text{factor (to)}} \\ \text{example} \ :\ 26.2 \, \text{mi to km} = \dfrac{26.2 \times 1{,}609.344}{1{,}000} = 42.164 \, \text{km} \end{gathered} \]
For speed, 1 mph = 1.609344 km/h and 1 knot = 1.852 km/h exactly.
Quick reference
| Metric | US customary |
|---|---|
| 1 km | 0.6214 mi |
| 1 m | 3.2808 ft |
| 1 kg | 2.2046 lb |
| 1 L | 0.2642 US gal |
| 100 km/h | 62.14 mph |
| 1 m² | 10.764 sq ft |
Note that the UK imperial gallon is 4.54609 L, about 20% larger than the US gallon. Fluid ounces and cups differ the same way.
3 real-life examples
A marathon in kilometers
26.219 miles × 1.609344 = 42.195 km.
A weight of 180 lb in kilograms
\( 180 \times 0.45359237 = \) 81.65 kg.
A 65 mph speed limit in km/h
\( 65 \times 1.609344 = \) 104.61 km/h.