Math
Unit Converter
Miles, pounds or gallons to metric and back, instantly
Type a value and pick the units to convert from and to: this unit converter handles length, weight, volume, area and speed between US customary and metric instantly.
The key idea
US units are not approximate: they are defined in metric
Since 1959, the inch has been exactly 2.54 cm and the pound exactly 0.45359237 kg. A mile is exactly 1,609.344 m, and a US gallon is exactly 3.785411784 liters. We use those exact factors, so the only rounding is on your screen.
How it is calculated
Each unit is first turned into the base unit of its kind (meter, kilogram, liter, square meter or meter per second) and then into the target unit.
Result = value × source factor / target factor
Exact definitions we use: 1 inch = 2.54 cm · 1 foot = 30.48 cm · 1 mile = 1.609344 km · 1 pound = 0.45359237 kg · 1 US gallon = 3.785411784 L. Cups, pints, quarts and fluid ounces are fractions of the US gallon (1 gal = 4 qt = 8 pt = 16 cups = 128 fl oz).
Worked example
10 miles = 10 × 1,609.344 / 1,000 = 16.0934 km. 150 pounds = 68.0389 kg. 5 US gallons = 18.9271 liters. 65 mph = 104.6074 km/h.
Official sources
Typical cases
US to metric conversion chart
The US units you use every day and their metric equivalent, both ways.
| US unit | Metric | Back to US |
|---|---|---|
| 1 inch | 2.54 centimeters | 1 centimeter = 0.3937 inches |
| 1 foot | 0.3048 meters | 1 meter = 3.2808 feet |
| 1 yard | 0.9144 meters | 1 meter = 1.0936 yards |
| 1 mile | 1.6093 kilometers | 1 kilometer = 0.6214 miles |
| 1 ounce | 28.3495 grams | 1 gram = 0.0353 ounces |
| 1 pound | 0.4536 kilograms | 1 kilogram = 2.2046 pounds |
| 1 stone | 6.3503 kilograms | 1 kilogram = 0.1575 stone |
| 1 fluid ounce (US) | 29.5735 milliliters | 1 milliliter = 0.0338 fluid ounces (US) |
| 1 cup (US) | 236.5882 milliliters | 1 milliliter = 0.0042 cups (US) |
| 1 quart (US) | 0.9464 liters | 1 liter = 1.0567 quarts (US) |
| 1 gallon (US) | 3.7854 liters | 1 liter = 0.2642 gallons (US) |
| 1 square foot | 0.0929 square meters | 1 square meter = 10.7639 square feet |
| 1 acre | 0.4047 hectares | 1 hectare = 2.4711 acres |
| 1 mile per hour | 1.6093 km/h | 1 km/h = 0.6214 miles per hour |
Save or share this table as an image Common questions
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54 cm. A 55-inch TV has a diagonal of 139.7 cm.
How many pounds are in a kilogram?
A kilogram is about 2.2046 pounds, and a pound is exactly 0.45359237 kg (453.59 grams). For a quick mental estimate, multiply kilograms by 2.2.
How many kilometers are in a mile?
A mile is exactly 1.609344 km. Going the other way, 1 km is about 0.6214 miles, so a 5K race is about 3.11 miles.
Why does a gallon on another site give a different number?
Because there are two gallons: the US gallon of 3.785 L and the British imperial gallon of 4.546 L. Both are here; check which one your source uses.
What about temperature?
Temperature has its own converter, because you cannot just multiply: you also have to add or subtract. Use the temperature converter for Fahrenheit, Celsius and Kelvin.
How many square feet are in an acre?
Exactly 43,560 sq ft, which is about 4,046.86 m² or 0.4047 hectares. A square mile is 640 acres.
Geometry and conversions
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