Unit Converter

Convert between metric and imperial units across eight categories and see the value in every unit at once.

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How to use the unit converter

Choose a category, enter a value and pick the units to convert from and to. The answer appears instantly, along with the conversion factor and a table showing your value in every unit of that category – handy when you are not sure which unit you need. All conversions run in your browser, so they are immediate even on a slow connection.

Categories and exact factors

Since the international yard and pound agreement of 1959, imperial and U.S. customary units are defined exactly in terms of metric units, so conversions are precise rather than approximate:

  • Length: 1 inch = 2.54 cm exactly; 1 foot = 0.3048 m; 1 mile = 1,609.344 m; 1 nautical mile = 1,852 m.
  • Mass: 1 pound = 0.45359237 kg; 1 ounce = 28.349523125 g; 1 stone = 14 lb.
  • Volume: 1 U.S. gallon = 3.785411784 L, while the UK (imperial) gallon is 4.54609 L – about 20% larger.
  • Area: 1 acre = 4,046.8564224 m²; 1 hectare = 10,000 m².
  • Speed: 1 mph = 1.609344 km/h; 1 knot = 1 nautical mile per hour.
  • Digital storage: a kilobyte (KB) is 1,000 bytes, whereas a kibibyte (KiB) is 1,024 bytes. This difference explains why a "1 TB" drive shows about 931 GiB in some operating systems.

Temperature is different

Temperature scales have different zero points, so they need formulas rather than a single multiplier:

°F = °C × 9/5 + 32    °C = (°F − 32) × 5/9    K = °C + 273.15

Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level. −40 is the one temperature that reads the same in Celsius and Fahrenheit.

Quick mental conversions

  • Kilometers to miles: multiply by 0.6 (more precisely 0.621).
  • Kilograms to pounds: double and add 10%.
  • Celsius to Fahrenheit: double and add 30 for a rough figure.
  • Liters to U.S. gallons: divide by about 3.8.

Frequently asked questions

How many centimeters are in an inch?

Exactly 2.54 centimeters, by international definition since 1959.

How do I convert Celsius to Fahrenheit?

Multiply by 9/5 and add 32. For example, 20 °C × 1.8 + 32 = 68 °F.

Is a US gallon the same as a UK gallon?

No. A US gallon is 3.785 liters and an imperial (UK) gallon is 4.546 liters.

Why does my hard drive show less space than advertised?

Manufacturers use decimal units (1 GB = 1,000,000,000 bytes) while some systems report binary units (GiB, 1,073,741,824 bytes).

Last reviewed 2026-10-27. This unit converter is provided for general information; verify important decisions with a qualified professional.