Free Online Unit Converter
Convert length, weight, temperature, area, volume and other common measurement units with instant results.
A unit converter turns a measurement in one system into its equivalent in another — length, weight, temperature, volume and speed — covering the conversions people run into constantly with recipes, product specs, travel and everyday math.
What is a unit converter, and what categories does it support?
It's a tool that converts measurements between units without needing to remember or look up a formula — length, weight, temperature, area, volume and speed cover the everyday conversions people search for most. Enter the value, pick the unit you're converting from, then the unit you want, and the result updates instantly, entirely in your browser with nothing to install.
How do you convert length units like inches, feet and miles to metric?
Select the source and target length units and enter the value — the underlying conversions are fixed ratios: 1 inch equals 2.54 centimeters, 1 foot equals 0.3048 meters, and 1 mile is approximately 1.609 kilometers. Converting in the other direction (centimeters to inches, meters to feet, kilometers to miles) uses the same ratios inverted.
How do you convert weight between pounds and kilograms, and temperature between Fahrenheit and Celsius?
For weight, 1 pound is approximately 0.4536 kilograms, and 1 kilogram is approximately 2.2046 pounds — select the two units and enter the value either direction. Temperature doesn't use a simple ratio like the others, since the two scales have different zero points: Fahrenheit to Celsius is (°F − 32) × 5/9, and Celsius to Fahrenheit is (°C × 9/5) + 32.
How do you convert volume and speed units?
For volume, 1 US gallon is approximately 3.785 liters (and 1 liter is about 0.2642 US gallons) — select gallons and liters as the source and target the same way as any other category. Speed works the same pattern too, converting between units like kilometers per hour and miles per hour.
Why does the world use two completely different measurement systems in the first place?
The metric system is a deliberate, dated invention: it was created during the French Revolution, when the National Assembly tasked the French Academy of Sciences with replacing the roughly 700 different, often locally-inconsistent units of measure then in use across France. The law establishing the decimal metric system was passed on 7 April 1795, defining the meter as one ten-millionth of the distance from the North Pole to the equator, and the kilogram as the mass of a cubic decimeter of water. Countries that industrialized on their own separate timelines — most notably the United States and, to a lesser extent, the United Kingdom — never fully switched over, which is exactly why a unit converter translating between the metric world and the inch-pound world is still something people need more than two centuries later.
Is Unit Converter free to use?
Yes. Unit Converter is completely free, with no sign-up and no usage limits.
Do I need to install any software?
No. Unit Converter runs directly in your web browser — nothing to download or install.
Is my data kept private?
Everything happens on your device. We never receive or store the file or text you enter into Unit Converter.