Free Unit Converters
Convert between metric and imperial units in a click. Change centimeters to inches, kilograms to pounds or Celsius to Fahrenheit, with exact conversion factors and a handy reference table for common values.
3 free tools
Which unit converter do I need?
Converting a height, a room size or a running distance? The length converter switches between millimeters, centimeters, meters, kilometers, inches, feet, yards and miles.
Reading a recipe, a parcel label or your bathroom scale? The weight converter handles milligrams, grams, kilograms, tonnes, ounces, pounds and stones.
Checking a weather forecast, an oven setting or a body temperature? The temperature converter converts between Celsius, Fahrenheit and Kelvin.
How accurate are our unit conversions?
Our converters use the exact definitions agreed internationally in 1959, not rounded approximations. One inch is exactly 2.54 centimeters, one pound is exactly 0.45359237 kilograms and one mile is exactly 1.609344 kilometers. Every other length and weight conversion is derived from these, so results are as precise as the numbers you enter.
Temperature works differently because the scales have different starting points. Fahrenheit equals Celsius × 9/5 + 32, and Kelvin equals Celsius + 273.15. That is why you cannot convert a temperature difference the same way you convert a temperature reading: a rise of 10°C is a rise of 18°F, not 50°F.
Each converter also includes a reference table of common values for quick lookups. For background on why two systems exist and which shortcuts are worth memorizing, read our guide to metric vs imperial units.
Tips for everyday conversions
Use mental shortcuts for estimates and exact factors for anything important. Multiplying kilometers by 0.6 gives miles closely enough for a road sign, and doubling Celsius and adding 30 gives a rough Fahrenheit reading, but medication doses, engineering drawings and official forms deserve exact numbers.
Watch out for units that share a name. U.S. and UK gallons and fluid ounces are different sizes, and a "ton" can mean a metric tonne (1,000 kg), a U.S. short ton (2,000 lb) or a UK long ton (2,240 lb).
Health tools are a common reason to convert. Our BMI calculator accepts both metric and imperial inputs, so you can enter height and weight in whichever units you know.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54 centimeters. To convert inches to centimeters multiply by 2.54, and to convert centimeters to inches divide by 2.54. For example, 180 cm is about 70.87 inches, or 5 feet 10.9 inches.
How do I convert kilograms to pounds?
Divide the number of kilograms by 0.45359237, or multiply by about 2.2046. For example, 70 kg is about 154.32 lb. For a quick estimate, multiplying by 2.2 is close enough.
At what temperature are Celsius and Fahrenheit the same?
At −40 degrees. Below that point the Fahrenheit number is lower than the Celsius number; above it, Fahrenheit is always the higher of the two.
Which countries use imperial units?
The United States uses U.S. customary units for most everyday measurements, and Liberia and Myanmar use them in part. The United Kingdom and Canada are officially metric but still use miles, pints, feet and pounds in daily life.