There are 29.6 ml in a US fluid ounce, and 28.4 ml in an Imperial fluid ounce. Both answers are correct, and which one you need depends on which fluid ounce the recipe means. An American fluid ounce holds 29.57 ml, which is usually rounded to 29.6 ml, and an Imperial fluid ounce holds 28.41 ml. The difference is about 4 percent, which does not matter in a soup and can matter in a cocktail or a precise sauce. This page gives you both tables, the examples, and the rule for knowing which fluid ounce you are dealing with.
The conversion table
| Fluid ounces | US millilitres | Imperial millilitres | Cups | Tablespoons |
|---|---|---|---|---|
| 1 fl oz | 29.6 ml | 28.4 ml | 1/8 cup | 2 tbsp |
| 2 fl oz | 59.1 ml | 56.8 ml | 1/4 cup | 4 tbsp |
| 3 fl oz | 88.7 ml | 85.2 ml | 3/8 cup | 6 tbsp |
| 4 fl oz | 118.3 ml | 113.7 ml | 1/2 cup | 8 tbsp |
| 6 fl oz | 177.4 ml | 170.5 ml | 3/4 cup | 12 tbsp |
| 8 fl oz | 236.6 ml | 227.3 ml | 1 cup | 16 tbsp |
| 12 fl oz | 354.9 ml | 341.0 ml | 1 1/2 cups | 24 tbsp |
| 16 fl oz | 473.2 ml | 454.6 ml | 2 cups | 32 tbsp |
| 32 fl oz | 946.4 ml | 909.2 ml | 4 cups | 64 tbsp |
The millilitre figures are rounded to one decimal place. The US column is based on 29.5735 ml per fluid ounce, and the Imperial column on 28.4131 ml.
Worked example 1: a cocktail recipe in millilitres
A cocktail recipe calls for 2 fluid ounces of gin, and your jigger is marked in millilitres. Two US fluid ounces is 59.1 ml, so measure 59 ml, or round to 60 ml — the difference of a millilitre will not change the drink. If the recipe is British and the fluid ounces are Imperial, 2 fluid ounces is 56.8 ml, so measure 57 ml. The difference between the two is about 2 ml, which is small, but in a cocktail the ratio of gin to vermouth matters, so use the figure that matches the recipe's origin. If the recipe gives millilitres as well, trust those and ignore the fluid ounces.
Worked example 2: a sauce that needs 4 fluid ounces
A sauce recipe calls for 4 fluid ounces of cream, and your jug is marked in millilitres. Four US fluid ounces is 118.3 ml, so measure 118 ml, or round to 120 ml. Four fluid ounces is also half a cup, which is easier to measure in a cup than in a jug, so if you have a cup measure, use that instead. The conversion is most useful when you have only a millilitre jug and the recipe is written in fluid ounces, which happens often with American recipes that are printed alongside a metric conversion.
Worked example 3: a can of drink and its label
A can of soda is labelled 12 fluid ounces, and the metric label says 355 ml. Twelve times 29.57 is 354.9, which rounds to 355, so the label is using US fluid ounces. A British can labelled 330 ml would be about 11.2 US fluid ounces, or 11.6 Imperial fluid ounces, and the difference is why a British can looks smaller than an American one. Checking a label is a good way to confirm which fluid ounce you are dealing with: if the millilitres divided by the fluid ounces is about 29.6, it is a US fluid ounce, and if it is about 28.4, it is Imperial.
Method and source
A US fluid ounce is defined as one 128th of a US gallon, which is 29.5735 millilitres. An Imperial fluid ounce is defined as one 160th of an Imperial gallon, which is 28.4131 millilitres. The two are different because the two gallons are different: a US gallon is 3.785 litres, and an Imperial gallon is 4.546 litres. The US fluid ounce is larger than the Imperial fluid ounce, but the US pint is smaller than the Imperial pint, because a US pint holds 16 fluid ounces and an Imperial pint holds 20. That is the quirk that catches people out: the fluid ounce and the pint do not scale the same way across the two systems, so you cannot convert a pint by converting its fluid ounces unless you know which system you are in.
Practical guidance
The first thing to check is which fluid ounce the recipe means. If the recipe is American, its fluid ounce is 29.6 ml. If it is British, its fluid ounce is 28.4 ml. If the recipe gives millilitres, use those directly and skip the fluid ounces. Buy a jug marked in both fluid ounces and millilitres, and use it for liquids; for dry ingredients, weigh them, because a fluid ounce is a measure of volume, not of weight, and an ounce of flour is not the same as a fluid ounce of water. When you scale a recipe, convert to millilitres first, do the multiplication, and convert back at the end, because millilitres are the smallest unit and the maths stays exact.
Frequently asked questions
How many millilitres are in 1 fluid ounce?
There are 29.6 ml in 1 US fluid ounce, and 28.4 ml in 1 Imperial fluid ounce. Use 29.6 ml if the recipe is American, and 28.4 ml if it is British. The difference is about 1 ml.
How many millilitres are in 8 fluid ounces?
There are 236.6 ml in 8 US fluid ounces, and 227.3 ml in 8 Imperial fluid ounces. Eight US fluid ounces is exactly 1 US cup, which is why the figure 237 ml is so familiar.
How many fluid ounces are in 100 ml?
There are about 3.38 US fluid ounces in 100 ml, and about 3.52 Imperial fluid ounces in 100 ml. For most cooking, 3 1/3 US fluid ounces is a good enough figure, but for a precise recipe, use the exact number.
Is a fluid ounce the same as an ounce?
No. A fluid ounce measures volume, and an ounce measures weight. A fluid ounce of water weighs about an ounce, which is where the confusion comes from, but a fluid ounce of honey weighs about 1.4 ounces, and a fluid ounce of oil weighs about 0.9 ounces. Never swap them.
How many millilitres are in 12 fluid ounces?
There are 354.9 ml in 12 US fluid ounces, and 341 ml in 12 Imperial fluid ounces. Twelve US fluid ounces is a standard can of soda, which is labelled 355 ml, and that is a good way to remember the figure.
What is bigger, a US fluid ounce or an Imperial fluid ounce?
A US fluid ounce is bigger. It holds 29.6 ml, while an Imperial fluid ounce holds 28.4 ml. The difference is about 4 percent, which is small, but it is the opposite of the pint, where the Imperial pint is bigger than the US pint.