This unit converter handles the conversions that come up most in everyday life, school and work: length, weight, volume, area, temperature, time, energy, power, angle, pressure, speed, force, frequency, torque, data storage, data transfer rate, voltage, current, resistance, charge, capacitance, inductance, conductance, fuel economy and electric car efficiency. Choose a category, enter a value and pick the units — the result appears as you type, along with the exact conversion factor so you can check it or reuse it.
How to use the unit converter
- Pick what you're converting — length, mass (weight), volume, area, temperature, time, energy, power, or one of the physics, electrical, data and fuel-economy categories.
- Enter the value. Negative numbers work for temperature.
- Choose the “from” and “to” units. The menus show only units that make sense for the category.
Conversion formula
Temperature: °C = (°F − 32) × 5/9 · °F = °C × 9/5 + 32 · K = °C + 273.15
Every unit except temperature is a fixed multiple of a base unit, so conversion is one multiplication. Temperature scales have different zero points, so they need an offset as well as a factor.
Worked examples
- 26.2 miles to kilometers: 26.2 × 1.609344 = 42.16 km
- 150 pounds to kilograms: 150 × 0.45359237 = 68.04 kg
- 350 °F to Celsius: (350 − 32) × 5/9 = 176.7 °C
- 2 liters to US cups: 2 ÷ 0.2365882 = 8.45 cups
Exact definitions used
| Unit | Defined as |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 12 in = 0.3048 m |
| 1 yard | 3 ft = 0.9144 m |
| 1 mile | 5,280 ft = 1,609.344 m |
| 1 pound | 0.45359237 kg |
| 1 ounce | 1/16 lb ≈ 28.3495 g |
| 1 US gallon | 231 in³ = 3.785411784 L |
| 1 US fluid ounce | 1/128 gal ≈ 29.5735 mL |
| 1 acre | 43,560 ft² ≈ 4,046.86 m² |
| 1 kWh | 3,600,000 J |
The length and mass definitions come from the 1959 international yard and pound agreement; the US gallon is defined as 231 cubic inches.
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 | 3.78541 |
| square feet | square meters | 0.09290304 |
| acres | hectares | 0.404686 |
US customary vs. imperial units
US and UK units share names but not always sizes. Inches, feet, yards, miles, ounces (weight) and pounds are identical. Volume units differ: the US gallon is 3.785 L while the UK imperial gallon is 4.546 L, and US and imperial fluid ounces and pints differ as well. This converter uses US units throughout. The ton also has several meanings — the US short ton (2,000 lb), the metric tonne (1,000 kg) and the UK long ton (2,240 lb).
Rounding and significant figures
A conversion cannot make a measurement more precise than it was. If a board is 2.5 m long to the nearest centimeter, saying it is 8.2021 feet long implies a precision nobody measured; 8.2 ft is the honest answer. As a rule of thumb, keep about the same number of significant digits as the least precise number you started with. The converter shows up to six decimal places so that you can copy a full-precision value when you need one, but rounding the final answer to match your input is good practice for school, shipping labels and recipes alike.
Temperature is different
Length, mass, volume and the other categories scale: doubling the number of miles doubles the kilometers. Temperature does not, because Celsius and Fahrenheit place zero in different spots. Water freezes at 0 °C but 32 °F, so you must shift by 32 before scaling by 5/9. Kelvin has the same step size as Celsius but starts at absolute zero, so K = °C + 273.15. A common mistake is to convert a temperature difference with the offset: a rise of 10 °C is a rise of 18 °F, not 50 °F, because differences only need the 9/5 factor.
Converting heights in feet and inches? Use the Height Converter. Converting recipe measurements with ingredient weights? Try the Cooking Conversion Calculator.
Frequently asked questions
How many kilometers are in a mile?
1 mile = 1.609344 kilometers exactly. To go the other way, 1 km = 0.621371 miles.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9: °C = (°F − 32) × 5 ÷ 9. So 100 °F = 37.8 °C. To convert Celsius to Fahrenheit, multiply by 9/5 and add 32.
How many pounds are in a kilogram?
About 2.2046 pounds. The pound is defined as exactly 0.45359237 kg.
Are US and UK gallons the same?
No. This converter uses the US gallon (3.785 L). The UK (imperial) gallon is larger, about 4.546 L, and US and UK fluid ounces and pints differ too.
How accurate are these conversions?
They use the exact definitions of each unit (for example 1 inch = 2.54 cm), so results are exact up to the rounding shown. Horsepower here is mechanical horsepower, 745.7 watts.