US fluid ounces to millilitres Converter

How many millilitres are in a US fluid ounce?

One US fluid ounce is 29.57353 millilitres. The full conversion is millilitres = US fluid ounces × 29.5735295625, and going the other way you divide instead of multiply.

A few anchor values worth memorising: 29.57353 ml to the US fluid ounce, 295.735296 ml to ten, and 2,957.352956 ml to a hundred. The calculator above handles the rest, including the awkward decimals.

The reference table under the converter lists the values people look up most often, so for a common figure you can read the answer off directly rather than typing anything.

Worked examples

Three worked examples, each multiplying by 29.57352956:

2.5 fl oz × 29.57353 = 73.9338 ml. 25 fl oz × 29.57353 = 739.3382 ml. 250 fl oz × 29.57353 = 7,393.3824 ml.

To reverse any of them, divide instead of multiplying — or use the swap button above, which does the same thing without the arithmetic. Reversing a converted value should return you to exactly what you started with; if it does not, something has been rounded too early.

Doing this conversion in your head

The exact factor is 29.57352956, which nobody multiplies by in their head. It is very close to 207/7, so multiplying by 207 and dividing by 7 lands within 0.01% of the correct answer — accurate enough for anything short of engineering work.

Since the factor is greater than one, the number always gets bigger: a US fluid ounce is smaller than a millilitre, so any quantity converts to more of them. If your answer came out smaller, you have divided when you should have multiplied.

That sanity check catches the majority of real conversion errors. Before trusting any converted figure, ask whether the direction of change makes sense — it takes a second and it is the single most effective safeguard there is.

When you need to convert US fluid ounces to millilitres

There are a handful of recurring contexts where a US fluid ounce figure has to be restated in millilitres.

On the source side, fluid ounces are US drink sizes and recipe measures. On the target side, millilitres are medicine doses, recipe liquids and drink container sizes. The conversion is essentially a translation between those two worlds — most often because a figure produced in one context has to be understood, submitted or acted on in the other.

Where the converted figure will be cut, dosed, billed or filed, round once at the end rather than at each step. For a rough sense of scale, round freely.

In every case the calculation happens on your own device. There is no request, no logging and nothing retained after you close the tab.

What a US fluid ounce and a millilitre actually are

The US fluid ounce (fl oz). The US fluid ounce is 29.57 ml; the UK version is 28.41 ml, which is a classic source of recipe errors.

The millilitre (ml). Equal to one cubic centimetre — the unit of medicine doses and recipes.

The two units describe the same physical quantity, volume, from different traditions. Once both were tied to the same defined standard, converting between them became exact arithmetic rather than measurement.

Common mistakes when converting US fluid ounces to millilitres

Watch out for the US/imperial split. The US gallon is 3.785 litres and the imperial gallon is 4.546 litres — about 20% larger. The fluid ounces differ too: 29.57 ml in the US against 28.41 ml in the UK. This converter uses US customary units, which is what almost all recipes published online assume.

Cups are worse still, because there are three in circulation: the US customary cup at 236.6 ml, the US legal cup at 240 ml used on nutrition labels, and the metric cup at 250 ml used in Australia and New Zealand. For baking, where ratios matter, weighing ingredients in grams sidesteps the whole problem.

If you are converting many values, change the source unit in the dropdown rather than converting through an intermediate unit. Every extra hop is another rounding opportunity.