Fluid Ounces to Milliliters

Bottles, cocktail measures, baby feeds and travel limits are quoted in fluid ounces in America and in millilitres almost everywhere else. A US fluid ounce is 29.5735295625 millilitres. The British one is not the same, which trips up more recipes than any other unit on this site.

How it is calculated

ml = fl oz × 29.5735295625

The US fluid ounce is a 128th of a US gallon, and the gallon is exactly 231 cubic inches, so the factor is exact. The imperial fluid ounce is 28.4130625 millilitres — smaller, despite the imperial gallon being larger, because it is divided into 160 parts rather than 128.

Source: NIST SP 811 (2008), Appendix B.8 — ounce (US fluid) (fl oz) to cubic meter (m³) = 2.957 353 E−05

Common values

Questions people ask

Is a fluid ounce the same as an ounce?

No. A fluid ounce measures volume, an ounce measures mass. They are close for water and nowhere near each other for anything else, which is why a recipe mixing the two produces surprises.

Why is the imperial fluid ounce smaller?

Because the two systems divide differently. The imperial gallon is larger than the US one, but it splits into 160 fluid ounces instead of 128. The result is that an imperial ounce is about 4 % smaller — the opposite of what the gallon sizes suggest.

What is the airline liquid limit in ounces?

The 100 millilitre cabin limit is 3.38 US fluid ounces, which is why containers are sold as 3 oz rather than 3.4 — rounding up would put them over.

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