Milliliters to Fluid Ounces
Convert millilitres to fluid ounces and back, for both the US and imperial fluid ounce — which are not the same size, and differ by about four per cent.
US fluid ounces (29.57 ml each). A UK fluid ounce is slightly smaller at 28.41 ml.
| Milliliters | US fl oz |
|---|---|
| 5 | 0.17 |
| 15 | 0.51 |
| 30 | 1.01 |
| 50 | 1.69 |
| 100 | 3.38 |
| 250 | 8.45 |
| 330 | 11.16 |
| 500 | 16.91 |
| 750 | 25.36 |
| 1000 | 33.81 |
The British gallon is 20% bigger. The British fluid ounce is 4% smaller.
Both are true at once, which the questions below note in passing and which is worth putting numbers to. Measured the same way round — British against American — the gallon is +20.09% and the fluid ounce is -3.92%. Turned around, the American fluid ounce is 4.08% larger than the British one. A unit is bigger and the unit it is built from is smaller, in the same pair of systems, at the same time.
| Unit | US | UK | UK against US |
|---|---|---|---|
| Gallon | 3,785.4118 mL | 4,546.09 mL | +20.09% |
| Pint | 473.1765 mL | 568.2613 mL | +20.09% |
| Fluid ounce | 29.5735 mL | 28.4131 mL | -3.92% |
The reason is division, not volume. Britain cuts its gallon into 160 fluid ounces and America cuts its smaller one into 128. A bigger cake into more slices gives smaller slices, and 160/128 is 1.25 — more than enough to overturn a 20.09% difference and leave 3.92% the other way. The arithmetic closes to the last bit a computer can hold: 1.20095 × 128/160 = 0.96076.
And the pint puts it back
A US pint is 16 fluid ounces and a UK pint is 20. Multiply the ounce ratio by 20/16 and the twenty per cent reappears: a British pint is 20.09% larger than an American one, exactly the gallon figure again, because 1.25 exactly undoes 128/160. Three units drawn from the same two systems and only the middle one inverts. Which is worth knowing before comparing any recipe, drink measure or bottle size across the Atlantic: the direction of the error is not constant.
| Shorthand | Against | Error |
|---|---|---|
| 30 mL to the ounce | US fluid ounce | +1.44% |
| 500 mL is a pint | US pint | +5.67% |
| 500 mL is a pint | UK pint | -12.01% |
Thirty millilitres to the ounce is close enough that no kitchen will notice. Half a litre as a pint is wrong by more than twice as much on one side of the ocean as the other, and in the opposite direction — it is over an American pint and under a British one.
968 of the first 1,000 whole millilitres do not survive a round trip
The factor above is the exact reciprocal of 29.5735295625 — the US gallon divided by 128 — so none of this comes from the constant. It comes from the display. Type a whole number of millilitres, read the ounces out and type them back and 968 of the first 1,000 fail to return. Going the other way, not one of the first 200 whole fluid ounces fails. A fluid ounce is thirty millilitres, so the same six decimals are generous in one direction and thin in the other.
How to use
- Pick US or imperial fluid ounces.
- Type a value in either box.
- Read the result to the precision your recipe needs.
- Remember a fluid ounce is a volume, not a weight.
Frequently asked questions
How many millilitres in a fluid ounce?
A US fluid ounce is 29.5735 mL; an imperial fluid ounce is 28.4131 mL. The imperial one is smaller, which is the opposite of the gallon relationship, because the imperial gallon is divided into 160 fluid ounces while the US gallon is divided into 128.
Is a fluid ounce the same as an ounce?
No. A fluid ounce measures volume and an ounce measures weight. They are close for water by coincidence of definition, and wrong for nearly everything else — a fluid ounce of honey weighs about 1.5 ounces, and a fluid ounce of oil weighs less than one.
What is a standard drink in millilitres?
It varies by country, which is why alcohol guidance rarely transfers. A US standard drink contains 14 g of pure alcohol, roughly 44 mL of 40 per cent spirit. A UK unit is 8 g, about 25 mL of the same spirit. Comparing weekly limits across countries without converting is meaningless.
How big is a shot?
In the US, typically 44 mL (1.5 fl oz). In the UK, a single is 25 mL and a double 50 mL by law. In much of Europe, 20 to 40 mL depending on the country. A cocktail recipe written in shots is therefore not portable.
What about a cup?
A US cup is 8 US fluid ounces, or 236.6 mL. A metric cup, used in Australia and New Zealand, is exactly 250 mL. An imperial cup was 284 mL. Recipes rarely say which, and the spread is large enough to affect baking.
How do I estimate quickly?
Treat 30 mL as one fluid ounce and you will be within two per cent for US measures. A 330 mL can is about 11 fl oz, and a 500 mL bottle is about 17.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.