Convert fl oz to cup

A US fluid ounce is 29.57 ml; a UK one is 28.41 ml. They are different units with the same name, and recipes rarely say which they mean.

A US customary cup is 236.6 ml, but American nutrition labels use a "legal" cup of exactly 240 ml, and a metric cup in Australia is 250. A recipe scaled up tenfold will show which one it assumed.

Going this way is a division, and by a whole number: 8 of these fit into one US cup with nothing left over. The awkwardness is only that the answers come out as fractions — a third of a US cup, a twelfth of one — rather than as the round figures the other direction gives you.

Nothing is lost to rounding even so. The division is exact, and if your answer will not sit still as a decimal — 0.0833… and friends — that is the fraction showing through, not an error creeping in.

The US fluid ounce is two different sizes wearing one name. This page uses the US one, which is 0.125 cup; the imperial one still used in the UK and Ireland is 0.12009 cup — smaller by 3.9 %.

That gap is the awkward size: far too big to ignore in a recipe, and far too small to spot from the answer alone. If your figure came from a British source, take the second number, and note that the fluid ounce is the one unit here where the imperial measure is the smaller of the two.

A US cup is 8 US fluid ounces, so the conversion is a division by eight and the useful figures come out clean: 2 fl oz is a quarter cup, 4 is a half, 6 is three quarters, 12 is a cup and a half, 16 is two cups and also a pint. Anything that is a multiple of two divides into something a measuring cup has a line for.

The trouble is that few containers are sold in multiples of eight. Evaporated milk comes in 12 fl oz, coconut milk in 13.5, broth in 14.5 and 32, water in 16.9 because it is really half a litre. Only the 12 and the 32 land on cup lines. Everything else leaves a remainder, and the remainder is where recipes get quietly rounded into being wrong — usually downward, because the leftover in the can is easier to ignore than to measure.

US labelling uses the same three letters for two unrelated quantities. A can marked 14.5 FL OZ holds 14.5 fluid ounces of liquid — a volume. A can marked 14.5 OZ carries 14.5 ounces of net weight, and how much space that occupies depends entirely on what is inside. Diced tomatoes, beans and condensed milk are usually labelled by weight; broth, juice and soda by volume.

The difference is not small enough to ignore. Fourteen and a half fluid ounces is 1.81 cups; 14.5 ounces of drained beans is closer to a cup and a half by volume, and 14.5 ounces of a dense syrup less again. Before dividing by eight, look for the word "fluid" or the letters FL on the label. If they are absent, the number is a weight and this conversion does not apply to it.

One fluid ounce is exactly two tablespoons, which makes the leftover part of any division easy to measure rather than guess. Take the whole cups first, then convert what is left: 13.5 fl oz is one cup with 5.5 fl oz over, and 5.5 fluid ounces is 11 tablespoons. Eleven is a half cup plus three tablespoons, so the can is one cup, one half cup, three tablespoons.

That route is more accurate than reading a fraction off the side of a jug, because a tablespoon is a fixed vessel and the meniscus in a glass measure is a judgement call. It also survives scaling: doubling 13.5 fl oz means doubling 11 tablespoons to 22, which is a cup and six tablespoons, and no fraction has to be simplified at any point.

The customary cup used in recipes is 236.59 ml, but American nutrition labels use a "legal" cup of exactly 240 ml, defined for that purpose. The 1.4 per cent gap is invisible in a single measure and shows up when a serving size on a package is compared against a cup measure in a drawer, or when a recipe is scaled by ten.

Outside the United States the word means something else again. Australia, New Zealand and Canada use a metric cup of 250 ml — six per cent larger than the US one — and Japanese recipes are written around a 200 ml cup, which is fifteen per cent smaller. A fluid-ounce figure converted through the wrong cup is out by more than most rounding, and the error compounds across a whole ingredient list.

An imperial fluid ounce is 28.4130625 ml and a US one is 29.5735295625, so the imperial unit is about four per cent smaller. Twenty of them make an imperial pint, against sixteen US fluid ounces to a US pint, which means the two systems disagree about the pint by a full fifth even though their ounces are close.

For this page the practical rule is short: if the source is British, Irish or older Commonwealth, divide by 8.33 rather than 8 to get US cups. Ten imperial fluid ounces is 1.2 US cups, not 1.25; a half-pint of 10 fl oz in a British recipe is 284 ml. The error is small on one ingredient and adds up on a custard or a batter where the ratio of liquid to flour is the whole point.

Most US liquid measures carry both scales, and they agree — the cup line at 1 sits at the 8 fl oz mark, 2 cups at 16, 4 cups at 32. Where a jug also shows millilitres, the third scale is usually rounded: a 1-cup line printed as 240 ml is the legal cup, and one printed as 235 or 237 is the customary one. Both are on sale, and neither jug is faulty.

Liquid and dry measures are not interchangeable in the way the shared scale suggests. A liquid jug is filled to a line below the rim so it can be carried; a dry cup is filled to the brim and levelled off. Pouring a fluid-ounce figure into a dry cup means filling it to the top, which is fine for water and a spill risk for anything you then have to move.

Halving is where the fluid ounce earns its place, because it stays a whole number long after the cup fraction has stopped being useful. Three quarters of a cup is 6 fl oz; half of that is 3 fl oz, which is 6 tablespoons — a measurable quantity, where "three eighths of a cup" is not a line on anything. A third of a cup is 2.67 fl oz, and the tablespoon count of 5⅓ is the form that actually gets used.

Doubling runs the other way and usually improves matters. Two 12 fl oz cans is 24 fluid ounces, which is three cups, one and a half pints, or three quarters of a quart — all clean. When a doubled recipe suddenly produces tidy numbers, that is the ladder reasserting itself, and it is a good sign the original quantities were chosen around a container rather than around a measure. It is also the cheapest reason to double something: the arithmetic gets easier at the same time as the yield goes up.