How it works
The US fluid ounce is defined from the US gallon: 1 US fl oz = 1/128 gallon = 29.5735295625 mL exactly. Bottles, cans, cosmetics and baby formula are often labelled in both units, and airport security’s liquid limit is 100 mL — about 3.4 fl oz.
The formula
fl oz = mL ÷ 29.5735295625 mL = fl oz × 29.5735295625Worked example. A 500 mL water bottle is 500 ÷ 29.5735 = 16.91 fl oz. A 330 mL can is 11.16 fl oz. An 8 fl oz baby bottle holds 8 × 29.5735 = 236.6 mL, the same as one US cup.
Quick reference table
| Millilitres | US fluid ounces | US fluid ounces | Millilitres |
|---|---|---|---|
| 5 mL | 0.1691 fl oz | 5 fl oz | 147.8676 mL |
| 15 mL | 0.5072 fl oz | 15 fl oz | 443.6029 mL |
| 30 mL | 1.0144 fl oz | 30 fl oz | 887.2059 mL |
| 50 mL | 1.6907 fl oz | 50 fl oz | 1,478.6765 mL |
| 100 mL | 3.3814 fl oz | 100 fl oz | 2,957.353 mL |
| 150 mL | 5.0721 fl oz | 150 fl oz | 4,436.0294 mL |
| 250 mL | 8.4535 fl oz | 250 fl oz | 7,393.3824 mL |
| 330 mL | 11.1586 fl oz | 330 fl oz | 9,759.2648 mL |
| 500 mL | 16.907 fl oz | 500 fl oz | 14,786.7648 mL |
| 750 mL | 25.3605 fl oz | 750 fl oz | 22,180.1472 mL |
| 1,000 mL | 33.814 fl oz | 1,000 fl oz | 29,573.5296 mL |
| 2,000 mL | 67.628 fl oz | 2,000 fl oz | 59,147.0591 mL |
US vs UK fluid ounces
The UK (imperial) fluid ounce is slightly smaller: 28.4131 mL. Most labels and recipes online use US ounces; a British recipe may not. Both are listed in the volume section of the unit converter.
Fluid ounces are not weight ounces
A fluid ounce measures volume; an ounce (oz) of weight is 28.35 g. They only match roughly for water-like liquids, so do not use this page to weigh flour or sugar.
Tracking how much you drink? See the water intake calculator.