Unit Converter

Free online unit converter. Convert length, weight, temperature, speed, area, and volume between metric and imperial units.

Convert between metric and imperial units across six categories: length, weight, temperature, speed, area, and volume. Useful for cooking, travel, science, engineering, and everyday conversions between different measurement systems.

Metric vs Imperial systems

The metric system (SI) is used by most countries worldwide and is the standard in science and medicine. It's based on powers of 10, making conversions straightforward (1 km = 1000 m, 1 kg = 1000 g). The imperial system is primarily used in the United States (and to some extent the UK for everyday measurements). The coexistence of both systems is a common source of confusion, and unit conversion errors have caused real-world disasters — including the loss of the Mars Climate Orbiter in 1999.

Most common conversions

  • Length: 1 inch = 2.54 cm | 1 foot = 30.48 cm | 1 mile = 1.609 km
  • Weight: 1 pound = 0.4536 kg | 1 ounce = 28.35 g | 1 stone = 6.35 kg
  • Temperature: °F = (°C × 9/5) + 32 | °C = (°F − 32) × 5/9
  • Speed: 1 mph = 1.609 km/h | 1 knot = 1.852 km/h
  • Volume: 1 US gallon = 3.785 L | 1 UK gallon = 4.546 L | 1 cup = 236.6 mL

Temperature: special case

Temperature is the only conversion on this list that uses an offset formula (not just multiplication). 0°C = 32°F = 273.15K. Body temperature is 37°C = 98.6°F. Water boils at 100°C = 212°F. The Kelvin scale is used in science because it has no negative numbers — 0K is absolute zero, the coldest possible temperature.

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