US and Imperial ounces are not the same size
Most oz-to-mL mistakes are really this one: the two systems use different ounces. Pick US for American recipes and drink sizes, Imperial for older British ones.
The same "8 fl oz" is about 9 mL smaller in Imperial. It rarely matters for a drink, but it adds up in a large recipe or a medicine dose.
Common US conversions
| Fluid ounces (US) | Millilitres | Everyday equivalent |
|---|---|---|
| 1 fl oz | 29.57 mL | a plain shot |
| 1.5 fl oz | 44.36 mL | a standard bar shot |
| 8 fl oz | 236.6 mL | 1 US cup |
| 12 fl oz | 354.9 mL | a soda can |
| 16 fl oz | 473.2 mL | 1 US pint |
| 33.8 fl oz | 1,000 mL | 1 litre |
A fluid ounce measures volume, not weight. It only equals a weight ounce for water; for flour, honey or oil the grams differ.
Common questions
How many mL are in a fluid ounce?
A US fluid ounce is 29.5735 mL. A UK (Imperial) fluid ounce is 28.4131 mL — about 4% smaller. US food labels round the ounce to an even 30 mL.
Why are US and UK fluid ounces different?
They come from different gallons. The US kept the older English wine gallon, while Britain redefined its gallon in 1824. The gap carries down to the ounce, so 20 US fl oz is not the same as 20 UK fl oz.
Is a shot 1 fluid ounce?
A US shot is usually 1.5 fl oz, about 44 mL. A plain 1 fl oz pour is 29.6 mL, which is why some recipes and jiggers mark both.
