This converter changes millilitres (ml) into fluid ounces (fl oz) and back again, with separate factors for US and UK (imperial) ounces. It is aimed at cooking, drinks, and product labels that mix metric and imperial volume units.
How it works
The two ounce systems use different exact values:
- 1 US fluid ounce = 29.5735 ml
- 1 UK (imperial) fluid ounce = 28.4131 ml
Pick the system, then the converter divides or multiplies accordingly:
- fl oz = ml ÷ factor
- ml = fl oz × factor
The relationship is linear and bidirectional — type in either field and the other updates instantly. Choosing the correct ounce matters: a US recipe and a UK recipe will give different ml for the same number of ounces.
Example
A US recipe needs 12 fl oz of stock.
12 × 29.5735 = 354.9 ml. The same 12 imperial ounces would be 12 × 28.4131 = 340.96 ml — about 14 ml less.
| Millilitres (ml) | US fl oz | UK fl oz |
|---|---|---|
| 100 ml | 3.381 | 3.520 |
| 250 ml | 8.454 | 8.799 |
| 500 ml | 16.907 | 17.598 |
All calculations run locally in your browser with no network requests.
Why the two systems diverge
The US and UK fluid ounce share a name but descend from different historical measurement traditions. The US system kept the old wine measure, which defined a gallon as 231 cubic inches. The UK later reformed its imperial system around a different gallon (approximately 277.4 cubic inches), which is larger. Because both systems divide their gallon into 160 fluid ounces (UK) or 128 (US), the individual ounce sizes landed at different values. The overall result is slightly paradoxical: the UK fluid ounce is the smaller of the two, yet a UK pint (20 oz) is larger than a US pint (16 oz).
This matters in practical cooking. A US tablespoon is exactly 14.787 ml (½ US fl oz), while a UK tablespoon is typically measured as 17.758 ml (≈ ⅝ UK fl oz). Scales and measuring cups sold in different markets are calibrated accordingly, which is why following a recipe from the other side of the Atlantic without checking the ounce system can shift quantities enough to affect the result — particularly in baking where liquid ratios are precise.
When to use each convention
- US fl oz — all American recipes, most bartending guides, US food-label nutrition facts (serving sizes), and product labels marked “fl oz” without further qualifier.
- UK / imperial fl oz — British and Irish recipes, some Australian and older Commonwealth recipes, and any product or guide that says “fl oz” with an explicit “imperial” label. Modern UK supermarket products and many UK recipes now use millilitres, so check the source date and country.
Common conversions at a glance
| Volume | US fl oz | UK fl oz |
|---|---|---|
| 30 ml | 1.014 | 1.056 |
| 100 ml | 3.381 | 3.520 |
| 240 ml (1 US cup) | 8.115 | 8.447 |
| 250 ml | 8.454 | 8.799 |
| 500 ml | 16.907 | 17.598 |
| 1 litre | 33.814 | 35.195 |
For everyday liquids between 30 ml and 1 litre the gap between the two systems is rarely more than a few percent, but for smaller amounts in precision recipes — or when scaling up to litres — it adds up. When in doubt, prefer working in millilitres end-to-end and only convert at the final step for presentation.