Unit Converter
This unit converter changes measurements between metric and US units, such as inches to centimeters, pounds to kilograms, gallons to liters and Fahrenheit to Celsius. It covers length, weight, volume, area, speed and temperature, using the exact definitions of each unit.
Result
12 in = 30.48 cm
| 1 in | 2.54 cm |
|---|---|
| 1 cm | 0.39370079 in |
Exact unit definitions; results show up to 8 decimal places.
How Unit Conversion Works
Each unit is a fixed multiple of a base unit: meters for length, kilograms for weight, liters for volume, square meters for area and meters per second for speed. To convert, multiply by the size of the unit you have and divide by the size of the unit you want:
Result = value × (size of “from” unit ÷ size of “to” unit)
Temperature is different, because the scales start from different zero points:
- °C = (°F − 32) ÷ 1.8
- °F = °C × 1.8 + 32
- K = °C + 273.15
Worked Examples
12 inches to centimeters: 12 × 2.54 = 30.48 cm
5 gallons to liters: 5 × 3.785411784 = 18.93 L
350 °F to Celsius (a common oven temperature): (350 − 32) ÷ 1.8 = 176.7 °C, usually rounded to 175 or 180 °C
Common Conversions
| From | To | Multiply by |
|---|---|---|
| inches | centimeters | 2.54 |
| feet | meters | 0.3048 |
| miles | kilometers | 1.609344 |
| pounds | kilograms | 0.45359237 |
| ounces | grams | 28.3495 |
| US gallons | liters | 3.785412 |
| US cups | milliliters | 236.588 |
| square feet | square meters | 0.09290304 |
| acres | hectares | 0.404686 |
| mph | km/h | 1.609344 |
Tips
US and imperial units differ
US and UK (imperial) gallons, pints and fluid ounces aren’t the same size. An imperial gallon is about 20% larger than a US gallon.
Weight versus volume
A cup of flour and a cup of water weigh different amounts, so you can’t convert cups to grams without knowing the ingredient. This converter handles weight to weight and volume to volume.
Building materials
For quantities of concrete, gravel or mulch in cubic yards, the concrete calculator and gravel calculator work in both US and metric units.
Frequently Asked Questions
How many centimeters are in an inch?
Exactly 2.54. The inch has been defined as 2.54 centimeters since the international yard and pound agreement of 1959, so 12 inches is exactly 30.48 cm.
How do I convert pounds to kilograms?
Multiply pounds by 0.45359237, the exact definition of the pound. 150 lb is 68.04 kg. To go the other way, divide kilograms by 0.45359237, or multiply by about 2.2046.
How do I convert Fahrenheit to Celsius?
Subtract 32, then divide by 1.8. 98.6 °F is (98.6 − 32) ÷ 1.8 = 37 °C. To convert Celsius to Fahrenheit, multiply by 1.8 and add 32, so 20 °C is 68 °F.
How many liters are in a gallon?
A US gallon is exactly 3.785411784 liters, because it's defined as 231 cubic inches. An imperial (UK) gallon is larger, at exactly 4.54609 liters, so check which one a recipe or fuel figure uses.
How many feet are in a mile?
5,280 feet, which is exactly 1.609344 kilometers. A nautical mile, used at sea and in aviation, is longer, at exactly 1,852 meters.
How many square feet are in an acre?
43,560 square feet, or about 4,046.86 square meters. A hectare is 10,000 square meters, about 2.47 acres.
How do I convert miles per hour to kilometers per hour?
Multiply by 1.609344. 60 mph is 96.56 km/h. To go from km/h to mph, divide by 1.609344, so 100 km/h is about 62.14 mph.
Related Calculators
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Sources & Assumptions
- National Institute of Standards and Technology (NIST) — Special Publication 811, Appendix B, conversion factors (exact factors for the inch, foot, mile, nautical mile and mile per hour; temperature formulas)
- NIST Office of Weights and Measures — Unit conversion
- Exact definitions used are 1 in = 2.54 cm, 1 lb = 0.45359237 kg, 1 US gallon = 231 cubic inches, 1 imperial gallon = 4.54609 L and 1 nautical mile = 1,852 m. Areas use the international foot. Temperature uses °F = °C × 1.8 + 32 and K = °C + 273.15.
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