How many mL in an ounce? US, UK and weight ounces
Three different things get called an ounce. Here is how many milliliters each one is, a chart for the sizes people look up, and how to tell which ounce a label means.
By Akash Yadav Updated 19 October 2026
Short answer
1 ounce is about 29.57 mL, if it is a US fluid ounce
In the US, a fluid ounce is exactly 29.5735295625 mL. Round it to 29.57 mL for everyday use, or to 30 mL if you only need a rough idea. That is the ounce on a US drink can, a baby bottle, a measuring jug or a cough syrup cup.
The trouble is that "ounce" can mean three things, and they are not the same size:
- US fluid ounce: 29.57 mL. A volume. Used in the US.
- UK (Imperial) fluid ounce: 28.41 mL. Also a volume, and about 3.9% smaller. You meet it in older British and Irish recipes.
- Ounce of weight: 28.35 g. Not a volume at all. This is the ounce on a bag of flour or a kitchen scale.
If you just want a number for your amount, the ounces to milliliters converter does it in one step. The rest of this guide is for when you are not sure which ounce you are looking at.
Chart
Ounces to mL chart, US and UK
These are the amounts people look up most. The US column is the one you want for anything bought or written in the United States.
| Fluid ounces | US (mL) | UK (mL) |
|---|---|---|
| 0.5 fl oz | 14.79 | 14.21 |
| 1 fl oz | 29.57 | 28.41 |
| 2 fl oz | 59.15 | 56.83 |
| 3 fl oz | 88.72 | 85.24 |
| 4 fl oz | 118.29 | 113.65 |
| 6 fl oz | 177.44 | 170.48 |
| 8 fl oz | 236.59 | 227.3 |
| 10 fl oz | 295.74 | 284.13 |
| 12 fl oz | 354.88 | 340.96 |
| 16 fl oz | 473.18 | 454.61 |
| 20 fl oz | 591.47 | 568.26 |
| 24 fl oz | 709.76 | 681.91 |
| 32 fl oz | 946.35 | 909.22 |
| 64 fl oz | 1892.71 | 1818.44 |
The gap grows with the amount. At 1 fl oz the two differ by about a milliliter; at 32 fl oz they differ by 37 mL, which is more than a tablespoon of liquid. Going the other way? The milliliters to ounces converter turns mL back into US fluid ounces.
Why two
Why the US and UK fluid ounces are different
Both countries kept the name and defined it differently. A US fluid ounce is 1/128 of a US gallon, and the US gallon is 231 cubic inches, which is exactly 3.785411784 liters (NIST Handbook 44, Appendix C). A UK fluid ounce is 1/160 of an Imperial gallon, and the Imperial gallon is exactly 4.54609 liters (Weights and Measures Act 1985, Schedule 1).
So the UK gallon is bigger, but it is cut into more ounces. That is why the UK ounce ends up smaller while the UK pint ends up larger: a UK pint is 20 UK fluid ounces (568 mL), and a US pint is 16 US fluid ounces (473 mL). Someone ordering a pint in London gets about a fifth more than someone in New York.
Both definitions are exact. The decimals end, so 29.5735295625 mL and 28.4130625 mL are not rounded figures. They are the full values.
Real sizes
Common cans and bottles in mL
Most of the ounce sizes you see in a US shop are designed around round numbers in one system or the other. That is why some of them land neatly in metric and some do not.
| Size | mL | What it usually is |
|---|---|---|
| 3.4 fl oz | 100.6 | Travel-size bottle (the airline liquids limit) |
| 8 fl oz | 236.6 | One US cup, a small carton of milk |
| 12 fl oz | 354.9 | Standard soda or beer can |
| 16 fl oz | 473.2 | One US pint, a tall can or pint glass |
| 16.9 fl oz | 499.8 | Half-liter water bottle |
| 20 fl oz | 591.5 | Single-serve soda bottle |
| 32 fl oz | 946.4 | One US quart, a sports bottle |
| 64 fl oz | 1892.7 | Half a gallon of milk or juice |
Two of these are metric sizes wearing an ounce label. A "16.9 fl oz" water bottle is a 500 mL bottle, and "3.4 fl oz" is how 100 mL gets printed on a travel bottle (100 mL is 3.38 US fl oz, rounded to one decimal on the label). The rest are ounce sizes first, which is why a 12 oz can is marked 355 mL rather than a round number.
Weight
When "oz" means weight, not volume
On a food packet, "8 oz" almost always means eight ounces of weight. A weight ounce is 28.35 grams, and grams do not turn into milliliters without knowing what the food is. Eight ounces of honey fills far less of a jug than eight ounces of cornflakes.
Water is the exception that causes the mix-up. A milliliter of water weighs very close to a gram, so for water the two ounces nearly agree:
- 1 US fluid ounce of water weighs about 1.04 ounces. Close, but about 4% heavier than an ounce.
- 1 UK fluid ounce of water weighs about 1.002 ounces. Almost exactly one. The Imperial system was built that way, around 10 pounds of water to the gallon.
- 8 ounces of water by weight is 226.8 g, so about 227 mL. Eight US fluid ounces is 237 mL.
For anything that is not water, weigh it. If a recipe gives ounces for a dry ingredient, use ounces to grams and a kitchen scale. For liquids measured in cups, cups to milliliters and ounces to cups cover the usual kitchen steps.
Labels
Why a label might say 30 mL
US nutrition labels are allowed to round. For the Nutrition Facts panel, the FDA treats 1 fluid ounce as 30 mL, a cup as 240 mL and a tablespoon as 15 mL (21 CFR 101.9(b)(5)(viii)). That rounding is for serving sizes only.
The amount in the container is a separate statement, and that one is converted properly. So a serving might say "1 fl oz (30 mL)" while the bottle says "500 mL" for 16.9 fl oz. Both are correct for what they describe.
In your head
A quick way to estimate
Multiply the US ounces by 30. It overshoots by about 1.4%, which is fine for a drink and close enough for most cooking. 8 fl oz × 30 = 240 mL, and the real answer is 236.6 mL.
If you need it closer, multiply by 30 and take away 1.4%. For a UK recipe, multiply by 28.4 instead. And if you are scaling a whole recipe, convert every measure the same way. A recipe that mixes US and UK ounces will drift by about 4% wherever the two meet.
Common questions
Ounce questions people actually ask
How many mL is half an ounce?
14.79 mL for half a US fluid ounce, which is exactly one US tablespoon. Half a UK fluid ounce is 14.21 mL. If the half ounce is a weight, it is 14.17 g, not milliliters.
Is 1 oz the same as 30 mL?
Not quite. 30 mL is the rounded figure US food labels use for serving sizes. The real US fluid ounce is 29.57 mL, so 30 mL is about 1.01 fl oz.
How many mL is 1.5 oz?
44.36 mL in US fluid ounces, the size of a typical US shot glass. A UK recipe's 1.5 fl oz is 42.62 mL. For 8 oz, the cup-sized amount, the chart above has both columns.
How many ounces is 100 mL?
3.38 US fluid ounces. Travel bottles print it as 3.4 fl oz.
How do I know if a recipe uses US or UK ounces?
Look at where it was written and what else it uses. A recipe that also gives cups and °F is American. One with gas marks, grams or "pints" in a British context is UK, and its oven settings may need the oven temperature guide too. If you cannot tell, the difference is about 4%, which matters in baking and barely anywhere else.
The factors behind every number here, and the documents they come from, are on the methodology page. For other liquid measures, the volume converters are all in one place.
Use it
Converters in this guide
- Ounces to Milliliters fl oz → mL
- Milliliters to Ounces mL → fl oz
- Cups to Milliliters cup → mL
- Ounces to Grams oz → g
Every figure in this guide is computed at build time from the same conversion engine as the converters it links to, and the factors behind it are the defining standards listed on the methodology page. Nothing here is typed by hand from a template.
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