Unit Converter
Choose what you are measuring, pick two units and type a value. Every factor comes from the official definitions, so inches, pounds and gallons convert exactly.
Formula: cm = in × 2.54
Unit conversion pages by measure
Length17
Weight11
Temperature4
Area3
Volume9
Speed5
Data size7
Time2
Pressure4
Energy2
How do you convert one unit into another?
Multiply by the factor that links the two units. Most factors are exact by definition because US customary units are defined in metric terms; temperature is the exception and needs an offset as well as a factor.
- 1 inch
- 25.4 mm
- 1 pound
- 0.45359237 kg
- 1 US gallon
- 3.785411784 L
One converter for every everyday measure
The card at the top works for any pair inside one measure. Choose length, weight, volume or another measure, then pick the unit you have and the unit you need. Typing on either side converts toward the other, the arrow button flips the direction, and the formula under the result shows the exact factor in use.
Popular pairs also have pages of their own, listed above by measure. Those pages add a ready-made table of common values and notes on where the units are used, for example tape-measure fractions on inches to mm or body weight on kg to lbs. When the pair you picked has such a page, a link to it appears under the card.
What the converter handles
- Length and area: millimeters to miles, square kilometers, hectares and acres.
- Weight: milligrams to metric tons, ounces, pounds and stone.
- Volume: milliliters and liters against teaspoons, cups, pints, quarts and US gallons.
- Temperature: Celsius, Fahrenheit and kelvin, with a check for values below absolute zero.
- Speed, pressure and energy: km/h, mph, knots, kPa, bar, psi, atm, kJ and kcal.
- Data size and time: bits to terabytes with a decimal or binary switch, seconds to hours.
Metric, US customary and imperial
Three systems still share the world's labels. The metric system, formally the International System of Units (SI), is used for almost all science and trade. The United States keeps customary units such as the foot, the pound and the gallon for daily life, and the United Kingdom mixes metric with imperial units like the pint, the stone and the mile.
Since the international yard and pound agreement of 1959, the yard has been exactly 0.9144 m and the pound exactly 0.45359237 kg. Every customary length and weight therefore converts to metric without any measured uncertainty. Volume is where the systems part ways: a US pint is 16 US fluid ounces, while an imperial pint is 20 imperial fluid ounces and about 20 % larger.
Temperature and data sizes are special cases
Most conversions are a single multiplication, so 0 of one unit is 0 of the other. Temperature scales start from different zero points: 0 °C is 32 °F, and kelvin starts at absolute zero, so the converter adds the offset as well as scaling. That is why 20 °C is 68 °F rather than twice anything.
Data units have the opposite problem: the same symbol has two readings. Storage makers use powers of 1,000, while many operating systems count in powers of 1,024 and still print KB, MB and GB. The international standard names for the binary sizes are KiB, MiB and GiB. Pick the reading that matches where your number came from; the MB to GB page shows both side by side.
Unit converter questions
How accurate is this unit converter?
The factors are exact definitions, such as 1 inch = 25.4 mm and 1 pound = 0.45359237 kg, so the only rounding is in how many digits are shown. Results keep up to eight significant digits.
Which units can I convert here?
Length, weight, temperature, area, volume, speed, data size, time, pressure and energy. Pick the measure first; the two unit menus then list every unit of that kind.
Why does a gallon convert differently in the UK?
The US gallon is 231 cubic inches, about 3.785 liters, while the imperial gallon used in the UK is 4.54609 liters. The converter uses the US gallon, cup and fluid ounce.
Is a ton here a metric ton or a US ton?
A metric ton (tonne) of exactly 1,000 kg. The US short ton is 2,000 lb, about 907 kg, and the UK long ton is 2,240 lb, about 1,016 kg.
Are kilobytes 1,000 or 1,024 bytes?
Both readings exist. The converter starts with the decimal one, 1 KB = 1,000 bytes, as storage makers use it, and a switch on the card changes to the binary 1,024 that many operating systems show.