A US cup contains 8 fluid ounces (fl oz), which is about 236.6 milliliters. That figure is for volume. A cup does not generally weigh 8 ounces: the ounce on a kitchen scale is a unit of weight, and ingredients differ in how much a cupful weighs. Water-like liquids come near the 8 fl oz = 8 oz rule; flour is about half of it.
How many fluid ounces are in a cup?
NIST lists the US cup as 0.2365882 liters and the US fluid ounce as 29.57353 milliliters. Dividing, 236.5882 ÷ 29.57353 = 8.000 (to three decimals), so one cup is 8 fl oz. The fluid ounce is the unit; the cup is simply 8 of them.
Cups to ounces chart
| US cups | Fluid ounces | Milliliters (exact NIST factor) | Also called |
|---|---|---|---|
| 1/8 cup | 1 fl oz | 29.6 | 2 tablespoons |
| 1/4 cup | 2 fl oz | 59.1 | 4 tablespoons |
| 1/3 cup | 2.67 fl oz | 78.9 | |
| 1/2 cup | 4 fl oz | 118.3 | |
| 3/4 cup | 6 fl oz | 177.4 | |
| 1 cup | 8 fl oz | 236.6 | half a pint |
| 1 1/2 cups | 12 fl oz | 354.9 | |
| 2 cups | 16 fl oz | 473.2 | 1 pint |
| 4 cups | 32 fl oz | 946.4 | 1 quart |
| 16 cups | 128 fl oz | 3,785.4 | 1 gallon |
Use cups to ounces or ounces to cups for other values, and cups to ml for metric. For 2 tablespoons per fluid ounce see tablespoons to cups.
What is the difference between fluid ounces and weight ounces?
They share a name and a symbol, but measure different things.
| Fluid ounce (fl oz) | Ounce (oz, avoirdupois) | |
|---|---|---|
| Measures | Volume | Weight (mass) |
| NIST value | 29.57353 mL | 28.34952 g |
| Used with | Liquids in cups, bottles | Items on a scale |
| 1 cup equals | 8 fl oz | Depends on the ingredient |
The avoirdupois ounce is the weight unit, 16 to the pound. Only for water-like liquids are the numbers close: assuming water weighs about 1 g per mL, one fluid ounce (29.57 mL) weighs roughly 29.6 g, near 1.04 oz.
How much does a cup of common ingredients weigh?
| Ingredient | 1 cup weighs | In ounces |
|---|---|---|
| All-purpose flour | 120 g | 4 1/4 oz |
| Granulated sugar | 198 g | 7 oz |
| Brown sugar, packed | 213 g | 7 1/2 oz |
| Confectioners' sugar | 113 g | 4 oz |
| Rolled oats (King Arthur) | 113 g | 4 oz |
These are King Arthur Baking's published values. A cup of flour is therefore 4 1/4 weight ounces, not 8. For grams, see cups to grams.
Worked examples
Example 1: a recipe says "12 oz of milk"
For a liquid, recipes almost always mean fluid ounces. 12 ÷ 8 = 1.5 cups, or 12 × 29.57 = 355 mL.
Example 2: how many ounces in 3/4 cup?
3/4 × 8 = 6 fl oz, which is 177.4 mL.
Example 3: a 16 oz bag of flour
16 weight ounces of all-purpose flour at about 4 1/4 oz per cup is 16 ÷ 4.25 ≈ 3.8 cups. Using the fluid ounce rule would wrongly give 2 cups.
Example 4: converting a bottle label
A 16.9 fl oz bottle: 16.9 ÷ 8 = 2.11 cups, or 16.9 × 29.57 = 500 mL.
Why do US labels say 240 mL for a cup?
For nutrition labeling, US regulation rounds household measures: a teaspoon is 5 mL, a tablespoon 15 mL, a cup 240 mL and a fluid ounce 30 mL (21 CFR 101.9(b)(5)(viii)). A labeled "1 cup (240 mL)" serving is therefore 1.4% larger than the 236.6 mL legal cup. For cooking the difference rarely matters; for a calculation using the NIST factors, use 236.588 mL.
Common mistakes
- Treating fl oz and oz as equal. They match only for water-like liquids.
- Assuming every country's units match. US and imperial volume units differ; see metric vs imperial.
- Forgetting the gallon ladder. 1 gallon is 16 cups; the gallon guide shows the other steps.