How Many mL Are in an Ounce?
By ToolNimba Editorial Team June 20, 2026 5 min read
Quick answer
There are 29.57 mL in 1 US fluid ounce and 28.41 mL in 1 imperial (UK) fluid ounce. For quick mental maths, most people simply round to 30 mL per ounce.
A fluid ounce (fl oz) measures volume, so this is a volume conversion rather than a weight one. The catch is that the United States and the United Kingdom define the fluid ounce slightly differently, which is why you will see two figures. Once you know which system a recipe, label or prescription is using, the conversion is exact and easy to repeat.
US vs imperial fluid ounce
The US fluid ounce is the one you meet most often online, in American cookbooks, and on US nutrition labels. It equals 29.5735 mL, which is almost always written as 29.57 mL. The imperial fluid ounce, used in the UK and some Commonwealth countries, is a touch smaller at 28.4131 mL, usually shown as 28.41 mL.
The difference is small for a single ounce, but it adds up across a full cup or pint, so it pays to know your source. Over a single ounce the gap is just over 1 mL, which rarely matters. Scale that to 16 fluid ounces, though, and US and imperial diverge by almost 19 mL, roughly a tablespoon and a half. For baking, cocktails or medicine dosing, that margin is enough to notice, so always confirm whether your recipe or label is American or British before you start. If you are working through American recipes you may also find our guide to how many ounces in a cup helpful for the next step up.
Fluid ounce systems compared
| System | 1 fluid ounce in mL | Rounded |
|---|---|---|
| US customary | 29.5735 mL | 30 mL |
| Imperial (UK) | 28.4131 mL | 28 mL |
| US food labeling | 30 mL (defined) | 30 mL |
Why labels say 30 mL
For US nutrition and supplement labels, regulators define 1 fluid ounce as exactly 30 mL to keep numbers tidy. That is why a bottle marked 8 fl oz may read 240 mL even though the true math gives about 237 mL.
Ounce to mL conversion chart
Use this chart for common amounts. The US column is the right one for most recipes and product labels you find in North America, while the imperial column applies to British recipes and older UK references. Notice how each US value is the same multiple of 29.57, so you can extend the table to any amount by multiplying that one factor.
Fluid ounces to milliliters
| Fluid ounces | US (mL) | Imperial (mL) |
|---|---|---|
| 1 fl oz | 29.57 mL | 28.41 mL |
| 2 fl oz | 59.15 mL | 56.83 mL |
| 4 fl oz | 118.29 mL | 113.65 mL |
| 6 fl oz | 177.44 mL | 170.48 mL |
| 8 fl oz (1 cup) | 236.59 mL | 227.30 mL |
| 12 fl oz | 354.88 mL | 340.96 mL |
| 16 fl oz (1 pint US) | 473.18 mL | 454.61 mL |
How to convert ounces to mL by hand
You do not need a calculator for a rough figure. To convert any number of US fluid ounces to milliliters, just multiply by 29.57. Here is a worked example for 5 US fluid ounces.
The reverse direction is just as simple. To turn milliliters back into US fluid ounces, divide by 29.57 (or by 30 for a quick estimate). So a 500 mL water bottle is about 16.9 US fluid ounces, and a 750 mL bottle of wine works out to roughly 25.4 US fluid ounces. Keeping both the multiply and divide factors in mind means you can move in either direction without reaching for a chart.
- Start with the amount in fluid ounces: 5 fl oz.
- Pick your conversion factor. For US fluid ounces, use 29.57 mL per ounce.
- Multiply: 5 times 29.57 equals 147.85.
- Read the result: 5 US fluid ounces is about 147.85 mL, or roughly 148 mL.
- For a quick estimate, multiply by 30 instead: 5 times 30 equals 150 mL, which is close enough for cooking.
An easy way to remember it
If you only ever memorize one number, make it 30 mL per fluid ounce. It is close enough for cooking, packing and everyday shopping, and it scales in your head without effort: 2 ounces is about 60 mL, 4 ounces about 120 mL, and a cup (8 ounces) lands near 240 mL. The true US figure of 29.57 mL is only about 1.4 percent smaller, so for most casual conversions the rounded version is perfectly fine.
Reach for the exact 29.57 mL figure only when precision matters, such as scaling a recipe up several times, measuring medicine, or mixing chemicals where small errors compound. A handy anchor for the imperial side is that a UK fluid ounce (28.41 mL) is very close to a flat 28 mL, which mirrors the 28.35 grams in a weight ounce. That near match is a coincidence of how the British units were defined, but it makes the number easy to recall.
Where this conversion matters most
Knowing the ounce to milliliter relationship is handy in everyday situations where one country measures in ounces and another in milliliters.
- Cooking and baking: converting US recipes into metric measuring jugs.
- Travel and packing: carry-on liquids are usually limited to 100 mL, which is about 3.4 US fluid ounces.
- Medicine and supplements: dosing cups often print both mL and fl oz, so it helps to cross check.
- Drinks and bartending: a US shot is around 44 mL, or 1.5 fluid ounces.
- Shopping: comparing a 12 fl oz can to a 355 mL one to confirm they are the same size.
Common mistakes to avoid
Most conversion errors come from mixing up units rather than bad math. Watch out for these.
- Confusing fluid ounces with weight ounces. A fluid ounce is volume; a weight ounce is mass. They are not interchangeable, and only the same substance like water lines them up closely. See how many grams in an ounce for the weight side.
- Using the wrong system. Applying 28.41 mL to a US recipe, or 29.57 mL to a UK one, throws off larger batches.
- Forgetting the label rule. A US label may round 1 fl oz to 30 mL, so its totals will differ slightly from the precise 29.57 figure.
- Assuming a cup is universal. A US cup is 236.6 mL while a metric cup is 250 mL, so do not treat them as equal.
When you need to switch between ounces, cups, pints and liters quickly, the volume converter handles every direction for you. It is also worth a look at how many cups in a quart once you are comfortable with the smaller units.
Convert any volume instantly
Skip the mental math and convert fluid ounces, milliliters, cups, pints and liters in one place with the tool below.
🧪 Try the free tool Volume Converter Free volume converter for liters to gallons, ml to cups, tablespoons and fluid ounces. Type in any unit and the rest update instantly with exact US factors.To sum up: 1 US fluid ounce is 29.57 mL and 1 imperial fluid ounce is 28.41 mL, with 30 mL serving as the friendly rounded shortcut. Pick the right system for your source, multiply by the matching factor, and your conversions will line up every time. Bookmark the chart above for the amounts you reach for most, and lean on the converter whenever you need an exact figure in a hurry.
Frequently asked questions
How many mL are in an ounce?
There are 29.57 mL in 1 US fluid ounce and 28.41 mL in 1 imperial fluid ounce. Both are commonly rounded to 30 mL for quick estimates. The figure you use depends on whether your recipe or label follows the US or UK system.
How many mL are in 8 fluid ounces?
Eight US fluid ounces equal about 236.59 mL, which is one US cup. In the imperial system, 8 fluid ounces come to roughly 227.30 mL. On US food labels you may see this rounded to 240 mL because of the 30 mL labeling rule.
Is a fluid ounce the same as a weight ounce?
No. A fluid ounce measures volume and a weight ounce measures mass. They only match up closely for water, where 1 fluid ounce of water weighs about 1 ounce. For other liquids the density differs, so do not convert one to the other directly.
Why is 1 ounce sometimes 30 mL?
For US nutrition and supplement labeling, regulators define 1 fluid ounce as exactly 30 mL to keep package numbers simple. The true measured value is 29.57 mL, so the rounded 30 mL version is slightly larger but easier to read on a label.
How do I convert ounces to mL quickly?
Multiply the number of US fluid ounces by 29.57 to get milliliters, or by 30 for a fast estimate. For example, 3 fluid ounces times 29.57 equals about 88.7 mL. For imperial ounces, multiply by 28.41 instead.
How many fluid ounces is 100 mL?
100 mL is about 3.38 US fluid ounces or 3.52 imperial fluid ounces. This is why the standard carry-on liquid limit of 100 mL is often described as roughly 3.4 ounces on travel websites and airport signage.