Universal Volume Converter

The gallon is where people get caught. This page lists both: the US gallon at 3.78541 litres and the imperial gallon at 4.54609, a fifth larger, which is why a British car's quoted fuel economy in miles per gallon flatters an American one by about twenty percent before anything else is considered. Those two figures are not house rounding — they're the values NIST publishes in Special Publication 811, its official guide to using the metric system, which lists 1 US gallon as 3.785 412 litres and 1 Canadian/UK Imperial gallon as 4.546 09 litres. The litre is the base and every column updates from it. Three of the entries carry trade-specific definitions worth knowing. The oil barrel is 158.987 litres, exactly 42 US gallons, a petroleum convention that has nothing to do with a 55-gallon drum or a 31.5-gallon beer barrel.

The US bushel at 35.2391 litres is a dry measure for grain and produce, not a liquid one. The cup at 0.236588 litres is the US customary cup of eight fluid ounces, which is not the 240 mL cup used on nutrition labels nor the 250 mL metric cup common in Australian recipes — small gaps that compound in baking. What this cannot do is reach mass. A cup of water weighs about 236 grams and a cup of sifted flour about 120, and since no density is requested anywhere, no output here is a weight. Petroleum volumes corrected to a 60 °F standard are likewise outside its scope.