How to convert units
- Choose a category: length, weight, temperature, volume, area, speed, time, data, pressure or energy.
- Enter a value and pick the units to convert from and to.
- The table below shows the value in every other unit of the category at once.
Handy conversions
- 1 inch = 2.54 cm · 1 foot = 30.48 cm · 1 mile = 1.609 km
- 1 kg = 2.205 lb · 1 lb = 453.6 g · 1 stone = 6.35 kg
- °F = °C × 9/5 + 32 · 0 °C = 32 °F · 100 °C = 212 °F
- 1 US cup = 236.6 ml · 1 US gallon = 3.785 l
- 1 acre = 4,047 m² · 1 hectare = 2.471 acres
Converting money instead? Use the Currency Converter.
Metric and imperial systems
The metric system (meters, kilograms, liters) is used by almost every country and by science worldwide. The United States still uses US customary units (inches, feet, pounds, gallons) in daily life, and the UK uses a mix, with miles on road signs, pints in pubs and stone for body weight. Converting accurately matters for recipes, travel, shipping, DIY projects and buying products from abroad.
Quick mental conversions
- Kilometers to miles: multiply by 0.6 (100 km ≈ 62 miles).
- Kilograms to pounds: double it and add 10% (70 kg ≈ 154 lb).
- Celsius to Fahrenheit: double it and add 30 for a rough estimate (20 °C ≈ 70 °F; exact is 68 °F).
- Liters to US gallons: divide by about 3.8.
- Inches to centimeters: multiply by 2.5 (exact is 2.54).
Temperature is different
Most units convert by multiplying by a fixed factor, but temperature scales have different zero points, so they also need an offset. That is why 0 °C is 32 °F rather than 0 °F, and why doubling a Celsius temperature does not double it in Fahrenheit. Kelvin uses the same step size as Celsius but starts at absolute zero, −273.15 °C.
Data storage units
Internet speeds are measured in bits per second (Mbps), while file sizes are in bytes. One byte is 8 bits, so a 100 Mbps connection downloads at most 12.5 megabytes per second. The data storage category converts between bits and bytes and between decimal (KB, MB, GB) and binary (KiB, MiB, GiB) units.
Most searched conversions
Jump straight to a dedicated converter with a chart: Celsius to Fahrenheit, kilograms to pounds and centimeters to inches. Each page includes a quick mental shortcut and a table of common values.
Frequently asked questions
How accurate are the conversions?
They use the exact international definitions (for example 1 inch = 2.54 cm and 1 pound = 0.45359237 kg) and show up to 8 significant digits.
Why are there two kinds of gigabytes?
Storage makers use decimal units (1 GB = 1,000,000,000 bytes), while operating systems often use binary units (1 GiB = 1,073,741,824 bytes). That is why a “1 TB” drive shows about 931 GB in Windows.
Are cups and gallons US or UK?
Cups, pints, quarts and the first gallon option are US customary units. The UK (imperial) gallon is listed separately and is about 20% larger.