The gallon (abbreviation "gal"), is a measure of volume.
Historically it has had many definitions, but there are three definitions in current use:
- The imperial gallon (≈ 4.546 L) which since metrication is used colloquially in the United Kingdom and semi-officially within Canada
- The United States (liquid) gallon (≈ 3.79 L)
- The lesser used U.S. dry gallon (≈ 4.40 L).
The gallon, be it the imperial or U.S. gallon, is sometimes found in other English-speaking countries. Most European Countries follow the metric system and measure volumes in litres - 1 litre = 1 dm^3.