Fluid ounces to millilitres
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A US fluid ounce is exactly 29.5735295625 millilitres. An imperial fluid ounce is exactly 28.4130625 millilitres. The US one is 4.08% larger, so which one a recipe means changes the answer.
And neither of them is the ounce this site is mostly about. A fluid ounce measures volume. The ounce of weight is 28.349523125 grams. They share a name and measure different kinds of thing, which is why "8 oz" in a recipe is genuinely ambiguous until you know what it is describing.
There are four things called an ounce
Two measure weight and two measure volume. Nothing in the word tells you which, so go by what is being measured.
| Which ounce | Measures | Exactly | Where you meet it |
|---|---|---|---|
| Standard ounce (avoirdupois) | Weight | 28.349523125 g | Food, packaging, body weight, postage |
| Troy ounce | Weight | 31.1034768 g | Gold, silver, platinum, gemstones |
| US fluid ounce | Volume | 29.5735295625 ml | US recipes, US drink sizes |
| Imperial fluid ounce | Volume | 28.4130625 ml | UK recipes, imperial pints |
Grams and millilitres cannot be compared directly either. A gram is a weight and a millilitre is a volume, so converting between them needs the density of whatever you are measuring. That is exactly the problem grams to cups works through, ingredient by ingredient.
Why an imperial fluid ounce of water weighs an ounce
This is the part that ties volume back to weight, and it is not a coincidence. The imperial fluid ounce was defined as the volume occupied by one avoirdupois ounce of water. So they line up almost exactly:
| One fluid ounce of water | Volume | Weighs in grams | Weighs in standard oz |
|---|---|---|---|
| Imperial | 28.4130625 ml | 28.4131 g | 1.0022 oz |
| US | 29.5735295625 ml | 29.5735 g | 1.0432 oz |
The imperial figure lands within 0.22% of one weight ounce. The US figure is 4.32% over, because the US fluid ounce descends from a different gallon and was never tied to a weight. That is why the old line about a pint weighing a pound fits imperial measures and only roughly fits American ones.
Fluid ounces to millilitres
Both systems, side by side, so a recipe that does not say which it means can still be read safely.
| Fluid ounces | US, in ml | Imperial, in ml | US, as water in oz |
|---|---|---|---|
| 0.5 fl oz | 14.79 ml | 14.21 ml | 0.52 oz |
| 1 fl oz | 29.57 ml | 28.41 ml | 1.04 oz |
| 2 fl oz | 59.15 ml | 56.83 ml | 2.09 oz |
| 3 fl oz | 88.72 ml | 85.24 ml | 3.13 oz |
| 4 fl oz | 118.29 ml | 113.65 ml | 4.17 oz |
| 5 fl oz | 147.87 ml | 142.07 ml | 5.22 oz |
| 6 fl oz | 177.44 ml | 170.48 ml | 6.26 oz |
| 8 fl oz | 236.59 ml | 227.3 ml | 8.35 oz |
| 10 fl oz | 295.74 ml | 284.13 ml | 10.43 oz |
| 12 fl oz | 354.88 ml | 340.96 ml | 12.52 oz |
| 16 fl oz | 473.18 ml | 454.61 ml | 16.69 oz |
| 20 fl oz | 591.47 ml | 568.26 ml | 20.86 oz |
| 24 fl oz | 709.76 ml | 681.91 ml | 25.04 oz |
| 32 fl oz | 946.35 ml | 909.22 ml | 33.38 oz |
| 64 fl oz | 1,892.71 ml | 1,818.44 ml | 66.76 oz |
Millilitres to fluid ounces
| Millilitres | US fl oz | Imperial fl oz | As water, in oz |
|---|---|---|---|
| 5 ml | 0.169 | 0.176 | 0.176 oz |
| 10 ml | 0.338 | 0.352 | 0.353 oz |
| 15 ml | 0.507 | 0.528 | 0.529 oz |
| 25 ml | 0.845 | 0.88 | 0.882 oz |
| 50 ml | 1.691 | 1.76 | 1.764 oz |
| 100 ml | 3.381 | 3.52 | 3.527 oz |
| 150 ml | 5.072 | 5.279 | 5.291 oz |
| 200 ml | 6.763 | 7.039 | 7.055 oz |
| 236.588 ml | 8 | 8.327 | 8.345 oz |
| 250 ml | 8.454 | 8.799 | 8.818 oz |
| 300 ml | 10.144 | 10.559 | 10.582 oz |
| 500 ml | 16.907 | 17.598 | 17.637 oz |
| 750 ml | 25.361 | 26.396 | 26.455 oz |
| 1,000 ml | 33.814 | 35.195 | 35.274 oz |
Telling which ounce a recipe means
- Liquids are fluid ounces. Milk, water, stock, oil given in "oz" in a US recipe are almost always fluid ounces.
- Dry ingredients are weight. Flour, sugar, butter and chocolate in ounces mean weight, and the standard ounce. Never troy.
- American source means US fluid ounces. British and older Commonwealth recipes mean imperial, which is 4% smaller.
- Precious metals are never fluid. A "1 oz" gold coin is a troy ounce of weight, and nothing on this page applies to it.
Frequently asked
How many millilitres is a fluid ounce?
A US fluid ounce is exactly 29.5735295625 ml, usually rounded to 29.57 ml. An imperial fluid ounce, used in the UK, is exactly 28.4130625 ml. The US one is 4.08% larger, so which you mean matters. Both are volumes and neither is the same thing as the ounce of weight, which is 28.349523125 grams.
Is a US fluid ounce the same as a UK one?
No. A US fluid ounce is 29.5735295625 ml and an imperial one is 28.4130625 ml, a difference of about 4%. It goes the other way for pints: a US pint is 16 US fluid ounces at 473.18 ml, while an imperial pint is 20 imperial fluid ounces at 568.26 ml, making the imperial pint the larger of the two despite its smaller ounce.
Why does an imperial fluid ounce of water weigh about one ounce?
Because it was defined that way. The imperial fluid ounce was set as the volume occupied by one avoirdupois ounce of water, so the two line up to within about 0.22%. The US fluid ounce came from a different gallon and has no such relationship: a US fluid ounce of water weighs about 1.04 ounces. This is where the old rhyme about a pint weighing a pound comes from, and why it fits imperial measures better than US ones.
How many ml is 8 fl oz?
8 US fluid ounces is 236.588 ml, which is exactly one US customary cup. In imperial fluid ounces the same count is 227.30 ml. Note that a metric cup is 250 ml, so it holds 8.45 US fluid ounces rather than 8.
How many fluid ounces are in a litre?
A litre holds 33.814 US fluid ounces, or 35.195 imperial ones. Going the other way, 500 ml is 16.907 US fluid ounces and 250 ml is 8.454.