Unit Converter
Choose a category, pick the two units, and type a value. The other box updates as you type, and either box can be the one you edit: enter inches to get centimeters, or centimeters to get inches.
Where a unit has an international definition, the converter uses that exact value instead of a rounded one: 1 inch = 2.54 centimeters and 1 pound = 0.45359237 kilograms. Conversions are calculated in your browser, and results are shown to up to 12 significant digits.
Runs in your browser. Unit Converter processes your input on your own device. Nothing you enter or upload is sent to a server.
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(opens in a new tab)How to use the Unit Converter
- Choose a category: Length, Mass / Weight, Temperature, Speed or Area.
- Pick the From unit and the To unit. Each category starts with a sensible pair, and Swap units exchanges them.
- Type a number in either box. The other box shows the converted value as you type.
- Select Copy Result to copy a line such as 100 cm = 39.3700787402 in, or Reset to clear the numbers and restore the starting units.
Supported formats: Whole numbers, decimals, negative numbers and scientific notation such as 1e3. A single comma is read as a decimal comma, so 1,5 means 1.5.
Units it converts
| Category | Units |
|---|---|
| Length | Millimeters (mm); Centimeters (cm); Meters (m); Kilometers (km); Inches (in); Feet (ft); Yards (yd); Miles (mi) |
| Mass / Weight | Milligrams (mg); Grams (g); Kilograms (kg); Ounces (oz); Pounds (lb); Stone (st); Metric tonnes (t) |
| Temperature | Celsius (ยฐC); Fahrenheit (ยฐF) |
| Speed | Meters per second (m/s); Kilometers per hour (km/h); Miles per hour (mph); Knots (kn) |
| Area | Square millimeters (mmยฒ); Square centimeters (cmยฒ); Square meters (mยฒ); Square kilometers (kmยฒ); Square inches (inยฒ); Square feet (ftยฒ); Square yards (ydยฒ); Acres (ac); Hectares (ha); Square miles (miยฒ) |
Exact definitions behind the factors
Imperial and US customary units are defined in terms of metric ones, so the factors below are exact rather than rounded. A displayed result can still be rounded, because dividing by an exact constant does not always end.
| Definition | Category |
|---|---|
| 1 inch = 0.0254 meters | Length |
| 1 foot = 0.3048 meters | Length |
| 1 yard = 0.9144 meters | Length |
| 1 mile = 1609.344 meters | Length |
| 1 pound = 0.45359237 kilograms | Mass / Weight |
| 1 ounce = 0.028349523125 kilograms | Mass / Weight |
| 1 stone = 6.35029318 kilograms | Mass / Weight |
| 1 acre = 43560 square feet | Area |
| 1 hectare = 10000 square meters | Area |
| 1 mile per hour = 0.44704 meters per second | Speed |
| 1 knot = 1852 meters per hour, or one nautical mile per hour | Speed |
Temperature is not a simple factor
Length, mass, speed and area convert by multiplying or dividing. Celsius and Fahrenheit also start at different points, so converting uses an offset: ยฐF = (ยฐC ร 9/5) + 32 and ยฐC = (ยฐF - 32) ร 5/9. That is why -40 reads the same on both scales.
Popular conversions
If you already know the conversion you want, these pages open the converter with it selected and add the formula, a worked example and a table of common values. They are all listed at Unit Converters.
Things worth knowing
- Temperature supports Celsius and Fahrenheit only. There is no Kelvin.
- There are no volume units yet, because US and Imperial gallons, pints and fluid ounces differ and the converter will not guess which you mean.
- Mass means avoirdupois units: the pound and ounce here are not troy units, and pound-force is not converted.
- Thousands separators are not supported. A value such as 1,500 is rejected rather than guessed.
- Results are rounded for display to up to 12 significant digits.
Frequently asked questions
Are the conversions exact?
The unit definitions are exact wherever an international definition exists, such as the inch, the pound and the mile. The results are shown to up to 12 significant digits, so a long decimal is rounded for display even when the definition behind it is exact.
Can I type in the second box?
Yes. Either box can be edited. Type in the To box and the From box is calculated with the same engine in reverse.
What happens to my number when I swap units?
The number stays attached to its unit and the two rows trade places. The converter keeps the value you typed rather than a rounded copy of the result, so swapping repeatedly never changes it.
Why is 1,500 rejected?
A comma can be a decimal comma (1,5 is 1.5) or a thousands separator (1,500 is 1500), and the converter will not guess. Type 1500 or 1.5 instead. Thousands separators are not supported.
Why are there no gallons or fluid ounces?
US and Imperial gallons, pints and fluid ounces are different sizes, so a single "gallon" option could easily give a misleading result. Volume is left out until those units can be offered explicitly.
Is anything I enter sent to a server?
No. The conversion is calculated in your browser, and nothing you enter is sent anywhere.