Fluid ounces to ml:
multiply by 29.5735

How many millilitres are in a fluid ounce?

One US fluid ounce is 29.57352956 millilitres, or about 29.6 ml. It is a unit of volume, not weight, so it measures how much space a liquid takes up rather than how heavy it is.

The US fluid ounce is defined from the US gallon: a gallon is 128 fluid ounces and 3.785411784 litres, which gives the factor above. Eight fluid ounces make a US cup, and 33.814 fluid ounces make one litre.

The fluid ounces to ml formula

A second example runs in reverse. A 250 ml bottle is 250 × 0.0338140227 = 8.453506 fl oz, a little over one US cup. A 330 ml can is 11.15863 fl oz.

Chart: fluid ounces to millilitres

For amounts between rows, combine them. A 15 fl oz drink is 10 fl oz plus 5 fl oz, so 295.7352956 + 147.8676478 = 443.6029434 ml.

Where fluid ounces to ml is used

• Baby bottles: US bottles are marked in ounces, while formula guides abroad use millilitres. A 4 fl oz feed is about 118 ml.
• Skincare and travel: airline liquid limits are set in millilitres, and many US products show fluid ounces, such as a 3.4 fl oz bottle (100.6 ml).
• Drinks and bars: a US shot is often 1.5 fl oz, which is 44.36 ml.
• Medicine cups: dosing cups may show both units, but always follow the product label.

Quick estimates and a worked bottle example

When you do not have a calculator, use 30 ml per ounce for a fast mental answer and then adjust. For 8 fl oz, 8 × 30 = 240 ml, and the exact figure is 236.5882 ml. The shortcut overshoots slightly, so subtract a few millilitres if the amount matters.

Here is a practical case. A US water bottle is labelled 20 fl oz. The exact size is 20 × 29.57352956 = 591.4706 ml, so it is a little under 600 ml. If you drink 64 fl oz of water a day, that is 1,892.7 ml, or about 1.9 litres.

• 1 fl oz is about 30 ml
• 8 fl oz (one cup) is about 237 ml
• 16 fl oz (one pint) is about 473 ml
• 32 fl oz (one quart) is about 946 ml

Common mistakes with fluid ounces

• Confusing fluid ounces with weight ounces. A fluid ounce of honey weighs more than a fluid ounce of water, but both are the same volume.
• Using the UK ounce by accident. Imperial fluid ounces are about 4 percent smaller than US ones.
• Rounding 29.57 to 30 across many servings. On 100 fl oz that is already 43 ml of error.
• Using the factor the wrong way round. Millilitres are the smaller unit, so the ml number is always about 30 times larger than the ounce number.