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Unit Converter

Convert length, weight, speed, volume, temperature and 22 more kinds of units instantly — with exact definitions, the formula for every pair and results that update as you type.

How to use this tool

Steps for using the Unit Converter.

  1. Pick a category such as Length, Weight or Temperature — or search for a unit like “psi”, “cups” or “GiB”.
  2. Type a value into From and choose the units to convert between; the result updates as you type. Use the swap button to reverse the conversion.
  3. Set the decimal places, turn on Show formula to see the calculation, and copy, share or save the result to your recent conversions.
  4. Open a category page for its unit table, or a conversion page such as meters to feet for a full conversion table and worked examples.

Example

Kilometers to miles

Value
5.5 km
Result
3.417542 mi

Formula: mi = km ÷ 1.609344

Common use cases

  • Converting recipes, body measurements and travel distances between metric and US units.
  • Checking engineering, electrical and physics calculations.
  • Explaining storage sizes, tyre pressures or fuel economy figures from another country.

All 27 unit converters

Popular conversions

How the unit converter works

Every unit is stored with its exact definition relative to one base unit per category — the meter for length, the kilogram for mass, the kelvin for temperature. A conversion goes from the source unit to the base unit and from there to the target unit, so all 27 categories share one engine and there are no per-page formulas to drift out of date.

Most units are a simple scale factor, and the factors are exact where the unit is defined exactly: the inch is 2.54 cm, the pound 0.45359237 kg, the US gallon 231 cubic inches. Temperature scales also need an offset, because their zero points differ, and fuel consumption in L/100 km is the reciprocal of fuel economy — both are handled properly rather than with a single multiplier.

Results are calculated in double precision and normalised to 15 significant digits, which removes floating-point noise such as 0.30000000000000004. The decimal places you choose only affect what's shown. Impossible inputs, such as temperatures below absolute zero or a negative mass, show an error instead of a misleading number.

Units that share a name but not a size are kept apart: US and imperial gallons and fluid ounces, mechanical and metric horsepower, and decimal (GB) and binary (GiB) data units each have their own entry.

Limitations

  • Months and years aren't offered as time units because their length varies.
  • Absorbed radiation dose (gray) isn't converted to sieverts: that needs weighting factors.
  • The site has a light theme only, so the converter has no dark mode.

Frequently asked questions

How accurate are the conversions?

Each unit uses its official definition, and results are calculated in double precision (about 15 significant digits). Only the displayed value is rounded, to the decimal places you choose.

Why does temperature conversion use a formula instead of a factor?

Celsius, Fahrenheit and Kelvin have different zero points, so converting needs an offset as well as a scale: °F = °C × 9/5 + 32. Multiplying alone would give wrong answers.

Are my conversions stored anywhere?

Only in your own browser, if you save them to Recent conversions. Nothing you type is sent to a server, and you can clear the history at any time.

Is 1 GB 1,000 MB or 1,024 MB?

1 GB is 1,000 MB (decimal). The 1,024-based units are GiB and MiB — both sets are available and never mixed.