Cups to Ounces Converter

US cups to US fluid ounces — quick reference

The formula, worked line by line

The arithmetic is a multiplication by eight, and the eight is a definition. The US liquid gallon is exactly 231 cubic inches, which fixes it at 3.785411784 litres once the inch is 2.54 centimetres. Divide by 128 for the fluid ounce, and the cup is eight of those.

Because every link in that chain is exact, the conversion introduces no error of its own. Whatever inaccuracy reaches the bowl comes from the scoop, the level and the pour, which is a far larger source of variation than any decimal place this page could add.

fl oz = cups x 8
1 US cup = 8 US fl oz = 236.5882365 mL
1 cup -> 1 x 8 = 8 fl oz
0.5 cup -> 0.5 x 8 = 4 fl oz
cup = 8 fl oz = 16 tbsp = 48 tsp

Why the fractions stay clean and the thirds do not

Eight has factors of two and four but not three. Halves, quarters and eighths of a cup therefore land on whole fluid ounces, while thirds and sixths never can. Dropping to tablespoons fixes it, because a cup is 16 tablespoons and 16 is not divisible by three either, but 48 teaspoons is.

The weight ounce is a different unit

An avoirdupois ounce is 28.349523125 grams and a fluid ounce is a volume of about 29.57 millilitres. They are unrelated quantities that share a name. Converting between them requires the density of the specific substance, so a page that offers one factor for all ingredients is guessing rather than converting.

How to use the cups to ounces converter

A US cup is exactly 8 fluid ounces, so the conversion is a multiplication by eight and the answers stay tidy. Half a cup is 4 fluid ounces, three quarters is 6, and a cup and a half is 12. Nothing here needs rounding, because the cup was defined as this quantity rather than measured against it.

The reason to convert at all is usually shopping or scaling. A recipe written in cups has to be matched against packaging sold in fluid ounces, or multiplied up to a batch size a container can actually hold. Once the cup is in ounces, every other US measure follows without a second lookup.

The third-cup is the exception worth knowing about. Three does not divide into eight, so a third of a cup is 2.64 fluid ounces and two thirds is 5.36. Recipes still use the measure constantly because a third-cup scoop exists, but the ounce figure will never be a round number no matter how you write it.

Scaling is where the multiplication earns its keep. A recipe calling for three cups of stock needs 24 fluid ounces, which is not quite a full quart carton of 32. Four cups is a quart exactly. Knowing which container a batch fits into before starting saves an unplanned trip out for a second carton.

The third-cup problem

Every other common cup fraction divides cleanly into eight fluid ounces. A half is 4, a quarter is 2, an eighth is 1, and three quarters is 6. The third is the outlier, because eight divided by three does not terminate. A third of a cup is 2.6667 fluid ounces, which displays here as 2.64 when the input is written as the usual 0.33.

That small gap between 0.33 and a true third is worth naming rather than hiding. A recipe means one third exactly, so the honest figure is 2.67 fluid ounces. Typing 0.33 gives 2.64, an understatement of about one percent. On a single ingredient it disappears; on a tripled recipe it is a tenth of an ounce.

The same reasoning rescues two thirds, which is 10 tablespoons plus 2 teaspoons. Any time a cup fraction refuses to give a clean ounce figure, dropping down to the spoon ladder gives an exact answer instead of a rounded one, because 16 and 48 have factors that 8 does not.

Which cup is on the page

This converter uses the US customary cup of 236.59 millilitres, which is what an American recipe means. It is not the only cup in circulation. The metric cup used in Australia and New Zealand is a round 250 millilitres, 5.67 percent larger, and the cup the FDA defines for nutrition labelling is 240 millilitres, 1.44 percent larger.

Only one of those three is a customary unit; the other two were chosen to be round numbers. The labelling cup is set out in the Code of Federal Regulations alongside a 15 millilitre tablespoon, a 5 millilitre teaspoon and a 30 millilitre fluid ounce, all of them deliberate roundings rather than exact conversions.

For most cooking none of this matters, because a 5.67 percent error in a soup is invisible. It matters in baking, where the ratio between liquid and flour decides the result. Applying one cup definition to the liquid and another to the flour is the error worth avoiding, and using a single tool throughout prevents it.

Every US cups value, worked out

34 common US cups 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