Volume Converter

Convert between litres, gallons, cubic metres, and other volume units — including the US and UK gallon difference.

Why a Gallon Isn’t Always the Same Gallon

Volume conversion holds one genuine trap that catches people constantly: the US gallon and the UK imperial gallon are not the same size, with the imperial gallon being roughly twenty percent larger. This split happened because the two systems standardized volume differently — the UK gallon was defined from the volume of ten pounds of water, while the US gallon traces back to an older English wine-trade measure that the UK itself abandoned when it standardized in 1824, leaving the United States using the older, smaller definition ever since. This means a recipe, fuel tank capacity, or fluid volume figure quoted in gallons is genuinely ambiguous without knowing which country’s gallon is meant, and getting it wrong isn’t a rounding error, since the difference is large enough to matter in almost any practical context. The metric side is far more consistent, since a litre is defined as exactly one thousand cubic centimetres, meaning it connects cleanly to length measurements — a cube ten centimetres on each side holds exactly one litre — which is one of the genuine conveniences of the metric system that imperial volume units never quite achieved.