Fluid Ounces to mL Converter

US fluid ounces to milliliters — quick reference

The formula, worked line by line

This is a multiplication by a constant that was defined rather than measured, and the chain behind it is short. The 1959 International Yard and Pound Agreement fixed the inch at exactly 2.54 centimeters. The US liquid gallon is exactly 231 cubic inches, which makes it exactly 3.785411784 liters. Divide that by 128 and the fluid ounce is exactly 29.5735295625 milliliters.

Because every step is exact, the decimal terminates rather than repeating and the conversion adds no error at all. Any inaccuracy in the final quantity comes from the jug, the spoon or the pour, which is worth remembering before quoting a converted figure to more decimal places than a kitchen can measure.

mL = US fl oz × 29.5735295625
29.5735295625 = 3 785.411784 ÷ 128   (the US gallon, split 128 ways)
8 fl oz → 8 × 29.5735295625 = 236.588236 mL
US cup = 8 fl oz · pint = 16 · quart = 32 · gallon = 128
imperial mL = imperial fl oz × 28.4130625

The 30 mL shortcut and where it stops working

Treating a fluid ounce as 30 mL is the rounding almost everyone uses, and it runs about 1.44 percent high. On a single tablespoon or a single shot the error is a fraction of a milliliter and completely invisible. Scaled up it becomes real: a gallon converted at 30 mL per fluid ounce comes out 54.6 mL over, which is nearly four tablespoons.

Why this cannot tell you the weight

A milliliter is a cubic centimeter and a fluid ounce is a fixed number of them. Neither carries any information about mass, so converting to grams requires the density of the specific liquid, which changes with the substance and with temperature. There is no universal factor and any tool offering one is guessing on your behalf.

Water is the near miss that starts the confusion. Close to 4 degrees Celsius water is about one gram per milliliter, so a US fluid ounce of it weighs roughly 29.57 grams, which is 1.04 avoirdupois ounces rather than 1.00. Honey is far denser and oil is lighter, so for those the volume figure and the weight figure separate immediately.

How to use the fluid ounces to mL converter

An American quantity has to be measured with metric equipment. That is the situation this page is built for: a US recipe in front of a metric measuring jug, a formulation written in fluid ounces that has to be bottled to a metric label, or a drink recipe that assumes a jigger nobody in the room owns. One multiplication puts the number back into a unit your equipment can show.

Type the fluid ounces and the milliliters appear as you type. The tool multiplies by 29.5735295625, the exact US fluid ounce, which comes from the US gallon of exactly 3.785411784 liters split into 128 parts. That definition traces back to the 231 cubic inch gallon and the 2.54 centimeter inch fixed in 1959, so nothing along the chain is approximate.

The US measures form a clean ladder once you have the fluid ounce, because every rung is a whole multiple of the one below. A tablespoon is half a fluid ounce, a cup is eight, a pint is sixteen, a quart is thirty-two and a gallon is a hundred and twenty-eight. Convert the fluid ounce once and every other measure follows without a second lookup.

Rounding is the practical decision here, because 236.59 mL cannot be poured accurately into a jug marked every 25 mL. Rounding a cup up to 240 mL adds about 1.44 percent, and rounding down to 235 takes off about 0.67 percent. Either is fine once, and neither is fine repeated across eight ingredients in the same direction.

Measuring a US recipe in a metric jug

The converted numbers are almost never round, and metric jugs are graduated in round increments. A cup is 236.59 mL, a half cup is 118.29 and a quarter cup is 59.15, none of which line up with a mark on a jug that steps in 25 or 50 mL. That mismatch, not the arithmetic, is what makes an American recipe awkward to cook from in a metric kitchen.

The fix is to round once rather than repeatedly. Convert every quantity in the recipe, then decide on a single rounding convention and apply it to all of them in the same direction, so the ratios between ingredients survive even if the absolute quantities shift slightly. Ratios are what a batter, a brine and a dough actually depend on.

Small quantities are where a jug stops being the right tool altogether. Below about 50 mL the graduations are too coarse to read, and a set of spoons is more accurate: a US tablespoon is 14.79 mL against the 15 mL metric spoon, and a US teaspoon is 4.93 mL against the metric 5. Both are inside one and a half percent, which is why nobody bothers converting them.

Which fluid ounce did the recipe mean?

A recipe written in fluid ounces has to come from somewhere, and the two places it can come from disagree by 3.92 percent. The US fluid ounce is 29.5735295625 mL. The imperial fluid ounce, used in older British and Irish writing, is 28.4130625 mL, because the imperial gallon of 4.54609 liters is divided into 160 rather than 128.

The giveaway is the pint. A US pint is 16 fluid ounces; an imperial pint is 20. So a British recipe calling for half a pint means 10 imperial fluid ounces, which is 284.13 mL, while an American recipe calling for half a pint means 8 US fluid ounces, which is 236.59 mL. Those are different quantities by about a fifth.

Drink recipes carry the same split. An American jigger is 1.5 fl oz or 44.36 mL, and a large one is 2 fl oz or 59.15 mL, while British bars pour spirits by metric measure rather than by ounce. Cocktail proportions survive the translation as long as every ingredient in the same drink is converted with the same factor.

Every US fluid ounces value, worked out

27 common US fluid ounces figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask