The short answer: 1 cup = 8 fluid ounces. That single number is the whole conversion — multiply any amount in cups by 8 and you have the amount in fluid ounces. It is an exact conversion between two units of volume in the US customary system, so there is no estimating, no density to look up and no ingredient that changes it. A cup of water, a cup of milk and a cup of stock are all 8 fluid ounces.
Unlike a conversion between cups and grams, which depends on what is in the cup, this one has a single right answer. A cup is a defined volume and a fluid ounce is a defined volume, so the ratio between them is fixed by the definitions themselves. That makes it reliable in a way that ingredient conversions are not — and it means the table on this page is correct for every liquid, from water to cream to stock, without exception.
Conversion table
| Cups | Fluid ounces |
|---|---|
| ¼ cup | 2 fluid ounces |
| ⅓ cup | 2.6667 fluid ounces |
| ½ cup | 4 fluid ounces |
| ⅔ cup | 5.3333 fluid ounces |
| ¾ cup | 6 fluid ounces |
| 1 cup | 8 fluid ounces |
| 1.5 cups | 12 fluid ounces |
| 2 cups | 16 fluid ounces |
| 3 cups | 24 fluid ounces |
| 4 cups | 32 fluid ounces |
Read the table in either direction. Going from cups to fluid ounces, multiply by 8; going back, divide by 8 or multiply by 0.125. The middle rows are the ones recipes use most — ⅔ cup is 5.3333 fluid ounces, and 1 cup is 8 fluid ounces. If your amount is not in the table, multiply it by 8 and you have the answer. For a quick check: 1 cup is 8 fluid ounces, 2 cups are 16 fluid ounces, and 10 cups are 80 fluid ounces.
Worked examples
A cookie dough that needs ½ cup. The recipe calls for ½ cup and your jug is marked in fluid ounces. That is 4 fluid ounces — pour to that line and you have the right amount. If you double the recipe for a crowd, you need 1 fluid ounces, which is 8 fluid ounces. The conversion itself never changes with the ingredient: whether the cookie dough uses milk, water or melted butter, ½ cup is always 4 fluid ounces. What changes is only the weight, never the volume.
A small batch, halved. A onion gravy recipe makes too much, so you halve it. The original uses ¾ cup; halved, that is 0.375 cup, which is 3 fluid ounces. Small amounts are where conversion errors hurt most, because a 10% error in a small amount of liquid is a bigger share of the recipe. When the halved amount is awkward, measure it in fluid ounces — the finer unit gives you a cleaner number.
Baking, where precision matters. A cake batter that needs ¾ cup of milk has no room for guessing: that is 6 fluid ounces. In baking, liquid is a structural ingredient, and a 10% error changes the crumb. If your recipe gives the liquid in fluid ounces and your cups are in cups, convert before you start, not while the oven is heating. And if the recipe also gives a weight in grams, use the weight — it is the most accurate measure of all.
How the conversion works
The US cup is defined as 236.5882 ml, and the fluid ounce is defined as 29.5735 ml. Divide the first by the second and you get 8 — that is the whole derivation, and it is why the conversion is exact rather than approximate. No kitchen experiment was needed to establish it; the units were defined this way, so the ratio follows from the definitions. That is also why the same factor appears in every reliable conversion chart: there is only one right answer, and every source that uses US customary units agrees on it.
The one thing to check is which cup your recipe means. This page uses the US customary cup throughout. A metric cup is 250 ml, an imperial cup is 284 ml, and older recipes sometimes use a 'cup' that means whatever cup the writer had in the cupboard. If a recipe from outside the US gives an amount that looks wrong after converting — a cake with far too much liquid, a soup that is far too thin — the cup is the first suspect. Convert the recipe to grams once, write the grams on the recipe card, and the question never comes up again.
Rounding deserves a note too. The exact factor is 8 to four decimal places, and the full value runs further (236.59 ml divided by 29.57 ml). For everyday cooking, rounding to two or three significant figures is fine: a 1% rounding error is invisible in a soup and barely noticeable in a cake. But round only at the end. If you round the factor and then multiply by a large amount, the rounding error grows with the amount — so keep the full factor through the calculation and round the answer, not the factor.
Volume is not weight
A conversion between two volume units is the same for every ingredient, but a conversion between volume and weight is not — and confusing the two is the most common conversion mistake in cooking. A cup of all-purpose flour weighs about 120 g spooned and levelled (King Arthur Baking), a cup of granulated sugar about 198 g, a cup of butter about 227 g, a cup of milk about 244 g (USDA), and a cup of honey about 336 g. All of those weights are approximate, because they depend on how the ingredient is measured: flour is spooned and levelled, brown sugar is packed at about 213 g a cup, and honey is poured.
Flour weight is the most disputed conversion in baking. King Arthur Baking lists 120 g per cup spooned and levelled, while other sources quote 125 g, 130 g and up to 142 g for a scooped cup. We use the King Arthur spooned-and-levelled value as primary, and the gap is a warning: if you scoop flour instead of spooning and levelling it, you can add 20 g or more per cup, which is enough to make a cake dry. Granulated sugar carries a smaller dispute — King Arthur lists 198 g per cup and the USDA rounds it to 200 g, a difference of rounding rather than a real disagreement. When a recipe matters, verify with a kitchen scale: weigh the ingredient instead of measuring it by volume, and every dispute on this page disappears.
Small amounts and precision
Small measures are where conversions matter most, because the same absolute error is a bigger share of a small amount. A teaspoon that is off by a quarter is a 25% error; a cup that is off by a quarter is a 6% error. That is why baking recipes give leavening, salt and spices in teaspoons and tablespoons rather than cups: the small unit is the precise one. Use proper measuring spoons, not cutlery — a teaspoon from the drawer can hold anywhere from 3 ml to 7 ml, which makes the conversion meaningless. Level every spoon with a knife, and do not pack a spoon measure unless the recipe says packed. For amounts under a teaspoon, a pinch is about a sixteenth of a teaspoon and a dash is about an eighth, but those are estimates, not conversions, and they belong in seasoning, never in baking. If a recipe needs half a teaspoon and you only have a teaspoon measure, fill it halfway and level it — or weigh it, because a scale reads half a teaspoon of baking soda at about 2.3 g without any conversion at all.
Frequently asked questions
Is a US cup the same as a metric or imperial cup?
Not always, and this is the biggest trap in unit conversion. This page uses the US cup (236.5882 ml). A metric cup is 250 ml, an imperial cup is 284 ml, a US pint is 473 ml while an imperial pint is 568 ml, and an Australian tablespoon is 20 ml against the US 14.79 ml. If your recipe comes from outside the US, check which system it uses before converting — the factor on this page is correct for US measures only.
Can I use a kitchen scale instead of converting?
For liquids, often yes. A kitchen scale removes volume conversion entirely if the recipe gives grams, and for water-based liquids 1 ml weighs about 1 g, so millilitres and grams are nearly interchangeable. But the shortcut fails for fats and syrups: a cup of olive oil weighs about 216 g, not 237 g, and a cup of honey about 336 g. Use the scale when the recipe gives weights, and use this conversion when the recipe gives volumes.
Does temperature change the conversion?
No, not in any way that matters in a kitchen. Liquids expand slightly when heated, so a cup of boiling stock is a fraction of a percent larger in volume than a cup of cold stock, but the difference is far smaller than ordinary measuring error. Measure liquids at room temperature where you can, and never worry about temperature when converting between volume units.
How many cups are in 1 fluid ounce?
0.125 cup — the reverse of the main conversion. Divide the number of fluid ounces by 8, or multiply by 0.125. For example, 0.5 cup is 4 fluid ounces. Use the reverse direction when a metric recipe gives you fluid ounces and your cups are in cups.
How do I convert cups to fluid ounces without a calculator?
Multiply by 8; for a quick mental estimate, round the factor to a friendly number and accept a small error. If the factor is larger than 1, break the amount into whole units and fractions — for example, convert 2 cups and a half cup separately and add them. If the factor is smaller than 1, remember that one fluid ounce is 0.125 cup, which is often easier to picture. For anything that matters, a phone calculator or the table on this page is faster and more accurate than mental maths mid-recipe.