Is a US gallon the same as a UK gallon?

No. A US gallon is 3.785411784 litres while an Imperial (UK) gallon is 4.54609 litres, about 20 percent larger. Because of this, US and UK pints, quarts, and fluid ounces also differ, so always pick the right region.

How many millilitres are in a US cup?

A US cup is about 236.59 mL. A US fluid ounce is about 29.57 mL, and there are 8 fluid ounces in a cup. UK recipes often use a 250 mL metric cup instead, so check the source.

Why does the converter route through litres?

Each unit stores an exact litres-per-unit factor. Your value is converted to litres and then divided into the target unit, so all conversions share one base and avoid compounding rounding errors.

How big is a cubic metre in litres?

Exactly 1000 litres, since one litre is defined as one cubic decimetre. A cubic centimetre equals one millilitre, which is why those two units line up neatly in the table.

Are US and Imperial fluid ounces different?

Yes. A US fluid ounce is about 29.57 mL and an Imperial fluid ounce is about 28.41 mL. Confusingly the Imperial one is slightly smaller, even though the Imperial gallon is larger, because the two systems divide the gallon differently.

Volume Unit Conversion Reference

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Volume is where unit confusion bites hardest: the US and Imperial gallons differ, and so do their pints, quarts, and fluid ounces. This reference converts any volume into every supported unit at once, keeping US and UK measures clearly separate, with exact factors.

How it works

Each unit stores an exact number of litres per unit, with the litre as the shared base. Conversion is two steps:

litres = value × litresPerUnit[from]
result = litres ÷ litresPerUnit[to]

The key fork is the gallon: 1 US gallon = 3.785411784 L but 1 Imperial gallon = 4.54609 L. Each gallon is divided into its own quarts, pints, cups, and fluid ounces, so the US and UK families never share values. The SI side is clean: 1 L = 1 dm³, 1 mL = 1 cm³, and 1 m³ = 1000 L.

Tips and example

To convert 2 US gallons to litres: 2 × 3.785411784 ≈ 7.57 L.
A US recipe “cup” is ≈ 236.6 mL; many metric recipes use a round 250 mL cup instead — not the same thing.
For fuel economy comparisons, remember the gallon mismatch: a “40 mpg” UK figure is lower in US gallons.

Very large or very small results appear in scientific notation so the numbers stay readable.