OneStopWebTools

Unit Converter

Convert between metric, imperial and US customary units across ten categories, from centimetres and inches to kilowatt-hours and gigabytes. Each conversion shows the result in every unit of the category at once, using exact international definitions.

In every unit

Step-by-step guide: Common Unit Conversions: A Quick Reference

How to use the Unit Converter

  1. Choose a category, such as Length or Temperature.
  2. Enter the value and the unit you are converting from.
  3. Choose the unit to convert to. The result updates instantly; use Swap to reverse the direction.
  4. The table underneath shows the same value in every other unit of the category.

Example: a recipe and a road trip

  • An oven set to 180 °C is 356 °F: (180 × 9/5) + 32.
  • A 2-litre bottle holds 0.528 US gallons but only 0.440 UK (imperial) gallons — the two gallons differ by about 20%.
  • A 42.195 km marathon is 26.219 miles, because one mile is exactly 1.609344 km.
  • A 500 GB drive holds about 465.66 GiB, which is why computers often report less space than the box states.

Exact conversion factors

Each unit is defined relative to a base SI unit using the internationally agreed values, so conversions are exact rather than rounded approximations:

  • 1 inch = 2.54 cm exactly, so 1 foot = 0.3048 m, 1 yard = 0.9144 m and 1 mile = 1,609.344 m (international yard and pound agreement, 1959).
  • 1 pound = 0.45359237 kg exactly; 1 ounce = 1/16 lb; 1 stone = 14 lb.
  • 1 US gallon = 3.785411784 L; 1 imperial gallon = 4.54609 L.
  • 1 kilobyte (kB) = 1,000 bytes; 1 kibibyte (KiB) = 1,024 bytes.
  • Temperatures are converted through kelvin, using °F = °C × 9/5 + 32 and K = °C + 273.15.

Categories included

Length, mass, temperature, area, volume (metric, US and imperial), speed, data storage (decimal and binary), time, pressure and energy. Results are shown with up to 10 significant digits; very large or small values switch to scientific notation so precision is not lost.

Limitations to keep in mind

  • Cooking measures such as “cup” differ between countries; the converter uses the US customary cup (236.588 mL) and the metric cup (250 mL), labelled separately.
  • Month and year conversions in the time category use average lengths (30.436875 and 365.2425 days), so they are approximations for calendar purposes.
  • Floating-point arithmetic can introduce tiny rounding differences in the last displayed digit.

How your data is handled

Conversions run in your browser; nothing is sent or stored.

Frequently asked questions

Why are there two kinds of gallon?

The US gallon (3.785 L) and the imperial gallon used in the UK (4.546 L) have different historical definitions. Fuel economy figures in miles per gallon are therefore not comparable between the two countries.

What is the difference between GB and GiB?

A gigabyte (GB) is 1,000,000,000 bytes; a gibibyte (GiB) is 1,073,741,824 bytes. Drive makers use GB, while some operating systems report sizes in GiB but label them GB.

How do I convert Celsius to Fahrenheit in my head?

Double the Celsius value and add 30 for a rough answer. For 20 °C that gives 70 °F; the exact value is 68 °F.