The factor
fl oz = ml ÷ 29.5735295625. A US fluid ounce is 1/128 of a US gallon, which is defined as 231 cubic inches, so the factor is exact. Dividing by 30 gets close: 330 ml gives 11 against the real 11.16 fl oz.
Worked examples
Rounded to two decimal places:
| Millilitres | Fluid ounces (US) |
|---|---|
| 5 ml | 0.17 fl oz |
| 15 ml | 0.51 fl oz |
| 30 ml | 1.01 fl oz |
| 100 ml | 3.38 fl oz |
| 250 ml | 8.45 fl oz |
| 330 ml | 11.16 fl oz |
| 500 ml | 16.91 fl oz |
| 750 ml | 25.36 fl oz |
| 1,000 ml | 33.81 fl oz |
The 100 ml limit for liquids in cabin bags is 3.38 fl oz, which US rules round to 3.4.
US, not UK, fluid ounces
The converter knows the US fluid ounce only. A UK fluid ounce is 28.41 ml, about 4% smaller, so a UK figure comes out higher: 500 ml is 16.91 US fl oz but 17.6 UK fl oz. Fluid ounces measure volume, not weight; for weight, use Grams to oz.
Questions
How many ml are in an ounce?
29.57 ml in a US fluid ounce. US bottles and nutrition labels usually round it to 30 ml.
Is 1 ml of water 1 gram?
Very nearly, at room temperature, so 100 ml of water weighs about 100 g, which is 3.53 oz by weight.