Milliliters to Fluid Ounces
Source: NIST SP 811 Appendix B.9 with NIST Handbook 44 Appendix C for US customary, and the Weights and Measures Act 1985 Schedule 1 for Imperial · Source verified August 14, 2026
A volume conversion tool that turns metric milliliters (mL) into fluid ounces. One US customary fluid ounce is exactly 29.5735295625 milliliters and one Imperial fluid ounce is exactly 28.4130625 milliliters, both following from statutory definitions rather than measurement. A fluid ounce measures volume, unlike the ounce of mass used on a scale.
Start with a figure in milliliters and read it back in fluid ounces. Pick the US customary or Imperial fluid ounce, and the formula, the working, and the reference table all follow your choice.
Quick Answer
Divide milliliters by 29.5735295625 for US customary fluid ounces, or by 28.4130625 for Imperial. For example, 500 mL is 16.91 US fluid ounces.
Fluid ounce standard
1 US customary fluid ounce = 29.5735295625 mL. Switching changes every figure below.
This converts volume, not weight. A fluid ounce measures how much space a liquid takes up. An ounce on a kitchen scale measures mass, and the two only coincide for a liquid whose density happens to match water closely.
Answer in US customary fluid ounces
16.907 fl oz
500 mL ÷ 29.5735295625 = 16.907 fl oz
500 mL is 16.907 US customary fluid ounces. Because one fluid ounce is about thirty times a millilitre, a positive input gets numerically smaller in this direction.
The unit relationship is exact by definition. The calculator uses the full terminating decimal factor shown above, runs the calculation in double-precision floating point, and rounds the displayed result to six significant digits. The result is a volume in fluid ounces, not a weight.
Entered: 500 mL
Examples
100 mL
= 3.38 US fl oz
250 mL
= 8.45 US fl oz
500 mL
= 16.91 US fl oz
1,000 mL
= 33.81 US fl oz
How it works
Formula · US customary: fl oz = mL ÷ 29.5735295625 · Imperial: fl oz = mL ÷ 28.4130625
Going from millilitres to fluid ounces means dividing, because one fluid ounce is roughly thirty times the size of one millilitre. For a positive input the numerical value gets smaller in this direction, by a factor of about thirty.
US customary
fl oz = mL ÷ 29.5735295625
Imperial (UK)
fl oz = mL ÷ 28.4130625
Both divisors are exact rather than measured. They come from the definitions in the sources below, and each works out to a decimal that terminates. Anything shorter, such as 29.5735 or 29.57, is that same value rounded so it fits on a line.
Which fluid ounce do you mean?
“oz” on its own is ambiguous, and the three things it can mean are genuinely different quantities:
- US customary fluid ounce, 29.5735295625 mL. The default here, and what US recipes and drink labels mean.
- Imperial fluid ounce, 28.4130625 mL. The US fluid ounce is about 4.1% larger than this one. Used in older British and Commonwealth recipes.
- Ounce of mass, about 28.35 grams. A weight, not a volume. This page does not convert it, and no volume converter can, because the answer depends on what the liquid is.
Every answer on this page is a volume, not a weight. The similarity between 28.35 grams and 28.41 millilitres is a coincidence of two unrelated definitions. It is why the ounce of mass and the Imperial fluid ounce are so often confused, and why this page names the standard next to every result.
Working it out by hand
The divisor is not a measurement anyone took. It falls out of three definitions, each of which is exact, and the chain is short enough to walk end to end.
- An inch is defined as 2.54 cm, so a cubic inch is 2.54 × 2.54 × 2.54 = 16.387064 cm³, and a cubic centimetre is a millilitre.
- The US liquid gallon is defined as 231 cubic inches, so it is 231 × 16.387064 = 3,785.411784 mL.
- A gallon holds 128 fluid ounces, so one US fluid ounce is 3,785.411784 ÷ 128 = 29.5735295625 mL, with nothing left over.
The Imperial chain is shorter still. The gallon is defined directly as 4.54609 litres, and a fluid ounce is one one-hundred- and-sixtieth of it, so 4,546.09 ÷ 160 = 28.4130625 mL.
A worked conversion
Take 500 mL. Dividing by the US constant gives 500 ÷ 29.5735295625 = 16.9070113509. Two surfaces on this page shorten that, and they do it differently: the calculator above reports six significant digits, so it shows 16.907, while the reference table below rounds to two decimals and shows 16.91. Switching the standard to Imperial divides the same 500 mL by 28.4130625 instead, giving 17.5975 in the tool and 17.60 in the table. The US fluid ounce is about 4.1% larger than the Imperial one, which is the whole of why the two answers differ; neither calculation is wrong.
Milliliters to fluid ounces reference table
The millilitre figures on the left are the starting values. Both fluid-ounce columns are rounded to two decimal places, so they are equivalents rather than exact statements.
| Milliliters | US fl oz | Imperial fl oz | Note |
|---|---|---|---|
| 30 mL | 1.01 | 1.06 | Just over one US fluid ounce |
| 50 mL | 1.69 | 1.76 | |
| 100 mL | 3.38 | 3.52 | One tenth of a litre |
| 236.59 mL | 8.00 | 8.33 | Rounded millilitre equivalent of 8 US fl oz, one US customary cup |
| 250 mL | 8.45 | 8.80 | One quarter litre |
| 330 mL | 11.16 | 11.61 | |
| 355 mL | 12.00 | 12.49 | Approximately 12 US fl oz |
| 500 mL | 16.91 | 17.60 | Half a litre |
| 750 mL | 25.36 | 26.40 | Three quarters of a litre |
| 1,000 mL | 33.81 | 35.20 | One litre |
Rounding, and what a round trip costs you
The conversion is exact. The display is not, and the difference is worth naming because it is the only place a figure on this page can drift.
500 mL is 16.9070113509 US fluid ounces. Write that down to two decimals, as the reference table below does, and it becomes 16.91. Multiply 16.91 back by the same constant and you get 500.09 mL rather than 500. The 0.09 mL is the rounding you introduced when you wrote the answer down, not an error in either direction of the conversion. Convert back and forth several times, rounding each time, and the gap grows.
The calculator itself keeps more of the figure than that, which is why its own reverse check closes cleanly: it reports six significant digits, so 500 mL reads as 16.907 fl oz and multiplying that back returns 500 mL. The drift is a property of how far you round, not of the conversion.
The practical rule is the ordinary one: carry the unrounded value through any further arithmetic and round once, at the end. For cooking and for labels two decimals is far finer than the measuring equipment, so none of this matters. For anything where it might, keep the long figure.
Edge cases
- The standard is a choice, not an assumption. US customary is the default because it is what most people arriving here need, but the toggle changes every figure on the page and the result names which standard produced it. Nothing is silently assumed.
- A blank field waits. Clearing the input leaves the result empty rather than treating the blank as zero and printing a confident 0.00.
- Text that is not a number is refused. An entry like 12abc is rejected outright rather than being read as 12. That silent reading is a real failure mode in converters built on a loose parser, and this one does not do it.
- Negative volumes are refused. A volume below zero has no physical meaning, so the tool declines it rather than mirroring the sign into an answer.
- Millilitres and cubic centimetres are the same thing. A figure written in cc converts identically, with no adjustment.
- Density never enters into it. Both sides of this conversion are volumes, so the liquid does not matter. It would matter immediately if either side were a weight, which is why the ounce of mass is excluded here rather than quietly folded in.
Common mistakes
- Treating the answer as a weight. Fluid ounces measure volume. Converting to ounces on a scale needs the liquid’s density.
- Using the wrong standard. A recipe written in Britain before metrication means the Imperial fluid ounce, and the US fluid ounce is about 4.1% larger than that.
- Multiplying instead of dividing. Millilitres are the smaller unit, so the fluid-ounce answer must be a smaller number.
- Assuming a US cup is 250 mL. It is 8 US fluid ounces, which is 236.59 mL. The 250 mL cup is a separate metric convention.
Your figures stay in the page
The values you enter are processed by this page in your browser. They are not sent to a server, not stored after you close the tab, and not visible to anyone else. There is no account and nothing to sign up for.
Sources
The division itself needs no authority. What does is the three defining constants it rests on, and each is set by a body rather than chosen here. That is the whole of what these citations are for.
- NIST Special Publication 811, Appendix B.9, which gives the inch as exactly 2.54 cm. Combined with the US liquid gallon of 231 cubic inches in NIST Handbook 44, Appendix C, and 128 fluid ounces to the gallon, this fixes the US fluid ounce at 29.5735295625 mL.
- Weights and Measures Act 1985, Schedule 1, which defines the gallon as 4.54609 cubic decimetres and the fluid ounce as one twentieth of a pint. That gives the Imperial fluid ounce as 28.4130625 mL.
NIST also publishes a rounded 2.957 353 E-05 cubic metres for the US fluid ounce and does not mark that tabulated figure exact. It is the same definition shown to seven digits, not a competing value.
Related converters
- Fluid ounces to milliliters for the same relationship in the other direction, when you start from a fluid-ounce figure.
- Volume converter for cups, pints, quarts, gallons, litres, and cubic units.
- How many mL in a liter for the metric side on its own.
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