Conversion tool
Volume Converter
Convert between metric and US customary/imperial volume units. Note: US and imperial gallons differ — this converter uses exact NIST definitions for both.
Formula & conversion factors
1 US gallon = 3.785411784 L (exact, NIST SP811)
1 UK gallon = 4.54609 L (exact, by definition)
1 US fl oz = 1/128 US gallon = 29.5735 mL
1 US cup = 1/16 US gallon = 236.588 mL
Caution: US and imperial gallons differ by ~20%. A US gallon is 3.785 L; an imperial gallon is 4.546 L. This converter distinguishes them explicitly.
1 UK gallon = 4.54609 L (exact, by definition)
1 US fl oz = 1/128 US gallon = 29.5735 mL
1 US cup = 1/16 US gallon = 236.588 mL
Caution: US and imperial gallons differ by ~20%. A US gallon is 3.785 L; an imperial gallon is 4.546 L. This converter distinguishes them explicitly.
1Worked example: 2 litres in US cups. 2 ÷ 0.2365882365 = 8.4535 cups (roughly 8 and a half US cups).
Reference standard: Base unit: litre (L = 0.001 m³). US customary units per NIST SP811.
Imperial gallon defined as exactly 4.54609 L (Weights and Measures Act 1985, UK).
Common questions
What is the difference between a US gallon and a UK gallon?
A US liquid gallon is 3.785 L; an imperial (UK) gallon is 4.546 L — about 20% larger. This matters for fuel economy figures: US MPG and UK MPG are not the same.
How many ml are in a US cup?
Exactly 236.588 mL (one-sixteenth of a US gallon). This is the legal US cup used in nutrition labelling; it differs slightly from some older "metric cup" definitions (250 mL).