UnitUtils

About UnitUtils

What UnitUtils is

UnitUtils is a collection of free unit converters. It covers 14 kinds of measurement (length, weight, volume, temperature, area, speed, time, data, pressure, energy, power, force, angle and frequency), and 16 of the most requested conversions have a page of their own with the formula, a table of common values and worked examples.

Why it exists

Converting a unit is easy until the unit name is ambiguous. A gallon, a ton, a cup, a calorie, a gigabyte and a horsepower each mean more than one thing. UnitUtils names the version it uses on every page, keeps the versions apart, and shows the constant behind each result so you can check it.

Accuracy

  • Conversion factors are the exact legal or SI definitions wherever one exists: the inch is exactly 25.4 mm, the pound exactly 0.45359237 kg, the US gallon exactly 3.785411784 L and the nautical mile exactly 1,852 m.
  • All conversions go through one calculation engine. The converter, the tables on each page and the numbers in the text come from it, so they cannot disagree.
  • Results are rounded only to remove floating-point noise (12 significant digits), and the number shown is rounded to six significant digits by default. You can choose a different precision.
  • The engine is covered by automated tests that include exact definitions, reverse conversions, round trips, zero, very small and very large values, negative numbers where they make sense and temperature edge cases such as absolute zero.
  • Where a unit has no single fixed size, the page says so. Months and years appear only as labelled averages.

Independence and limits

UnitUtils is an independent website. It does not provide engineering, medical, legal, financial or other professional advice, and its results are not certified for any official purpose. For work where an error would be costly, check the figures against the standard that applies to you. See the terms of use.

Feedback

If a result looks wrong or a conversion is missing, please get in touch. A confirmed calculation error is treated as a bug and gets a regression test.