Cups to Gallons Converter
Convert between cups and gallons — US, imperial, and metric. Exact NIST and UK statutory factors, bidirectional, no rounding tricks.
1 US cups (customary, 8 fl oz) =
0.06
Converted via the millilitre pivot — 236.5882365 mL per us_cup, 3785.411784 mL per us_gal. US gal = 231 in³ exact (NIST SP 1038), imperial gal = 4.546 09 L exact (UK W&M Act 1985), US legal cup = 240 mL exact (21 CFR 101.9), metric cup = 250 mL exact (AS 1349).
How to use this calculator
Type a value, choose the cup or gallon type in "From", and the unit you want in "To". The result updates instantly. Switching the From and To selects flips the conversion direction.
How the calculation works
Every unit converts via an intermediate value in millilitres. The factors are exact: 1 US gallon = 231 cubic inches (NIST SP 1038) = 3 785.411 784 mL. 1 US customary cup is exactly 1/16 of a US gallon = 236.588 235 mL. The US legal cup used on nutrition labels is 240 mL exactly (21 CFR 101.9). A metric cup (Australia, New Zealand, Canada) is 250 mL exactly. 1 imperial gallon is 4 546.09 mL exactly (UK Weights and Measures Act 1985), so an imperial cup = 1/16 imp gal = 284.130 625 mL.
Worked example
8 US cups → US gallons: 8 × 236.588 235 mL = 1 892.71 mL ÷ 3 785.411 784 mL/gal = 0.5 US gal. The shortcut 8/16 = 0.5 works because a US cup is exactly 1/16 of a US gallon.
Frequently asked questions
How many cups are in a US gallon?
Exactly 16 US customary cups (1 cup = 8 fl oz, 1 gallon = 128 fl oz). If you use the US legal cup (240 mL) you get about 15.77 cups per gallon, and with a metric 250 mL cup you get about 15.14 cups per gallon.
How many cups are in an imperial (UK) gallon?
About 19.22 US customary cups, or exactly 16 imperial cups. An imperial gallon (4.546 09 L) is roughly 20% larger than a US gallon, which is where the difference comes from.
Is a US cup the same as a metric cup?
No. A US customary cup is 236.588 mL, the US legal cup (nutrition labels) is 240 mL exactly, and a metric cup (Australia, New Zealand, Canada) is 250 mL exactly. The differences are small but matter in baking — a metric cup of flour is about 6% more than a US cup.
Which cup should I use for an American recipe?
Use the "US cups (customary)" option — that is the cup used in almost every American cookbook. The 240 mL legal cup only appears on packaged-food nutrition panels and is not the cup recipes assume.
Why does the UK no longer use imperial cups?
British recipes mostly switched to weights (grams) and millilitres in the late 20th century, so imperial cups are rare. They are included here for historical recipes, Canadian imperial cookbooks, and rare UK conversions.
How accurate is this converter?
Conversions use the exact NIST and UK statutory factors and run in full floating-point precision. Display rounding is the only source of imprecision, and that is at the sub-millilitre level.