Calculators & everyday math
US vs. Imperial Volume Measurements
The US and the UK use the same names — gallon, pint, fluid ounce — for different volumes. The gaps are around 4 to 20 percent, easily enough to spoil a recipe or skew a comparison. This guide explains the differences and where they come from.
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Same names, different sizes
| Unit | US | Imperial (UK) | Imperial ÷ US |
|---|---|---|---|
| Gallon | 3.785411784 L | 4.54609 L | 1.200949926 |
| Pint | 473.176473 mL | 568.26125 mL | 1.200949926 |
| Fluid ounce | 29.57352956 mL | 28.4130625 mL | 0.9607599404 |
Why they differ
The US kept an older English wine gallon of 231 cubic inches. In 1824 Britain replaced its various gallons with the imperial gallon, originally the volume of 10 pounds of water, and it has been defined as exactly 4.54609 liters since 1985.
Pints and fluid ounces
An imperial fluid ounce is slightly smaller than a US one, yet an imperial pint is bigger — because an imperial pint holds 20 imperial fluid ounces while a US pint holds 16 US fluid ounces.
Avoiding mix-ups
- Check where a recipe comes from. UK recipes today mostly use metric measures; older ones may use imperial pints and fluid ounces.
- A pint of beer in a UK pub is an imperial pint of 568 mL.
- Fuel prices and fuel economy in the US use US gallons.
US vs. Imperial Volume FAQ
- Is a UK pint bigger than a US pint?
- Yes, about 20% bigger: 568.26125 mL against 473.176473 mL.
- Why is an imperial fluid ounce smaller when the pint is bigger?
- The imperial pint has 20 fluid ounces and the US pint only 16, so the pint comes out bigger even though each ounce is smaller.
- How many US fluid ounces are in an imperial pint?
- About 19.21519881.
- Are US and UK teaspoons different?
- The Volume Converter includes US teaspoons and tablespoons only; modern UK recipes generally use metric 5 mL and 15 mL spoons.
- Does the Volume Converter mix them up?
- No. Every gallon, pint, and fluid ounce is labelled US or imperial (UK).
Related guides
- Liters vs. GallonsThe exact size of the US and imperial gallons in liters, a conversion table for both, and why fuel economy figures differ between the US and UK.
- Cups, Pints, and QuartsHow US teaspoons, tablespoons, fluid ounces, cups, pints, quarts, and gallons fit together, in milliliters, and why there are three different cups.
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