The short answer
A US customary cup = 8 US fluid ounces = 236.588 mL.
But "8 ounces" is only true for volume. A cup of flour weighs about 4.25 oz; a cup of water weighs about 8.34 oz. Fluid ounces measure space; ounces measure mass. Recipes that say "8 oz of flour" mean weight, and using a measuring cup will nearly double the amount.
Cups are not standardized worldwide
| Cup | Milliliters | Fluid ounces |
|---|---|---|
| US customary | 236.588 mL | 8 US fl oz |
| US legal (FDA labels) | 240 mL | 8.12 US fl oz |
| Metric cup (AU, NZ, CA) | 250 mL | 8.45 US fl oz |
| UK cup (historic) | 284.131 mL | 10 imperial fl oz |
| Japanese cup (gō) | 200 mL | 6.76 US fl oz |
An Australian recipe's cup is 5.7% larger than an American one — enough to change a cake's crumb.
Weight per US cup, by ingredient
| Ingredient | Grams | Ounces (weight) |
|---|---|---|
| Water | 236.6 g | 8.35 oz |
| All-purpose flour (spooned) | 120 g | 4.23 oz |
| Bread flour | 127 g | 4.48 oz |
| Granulated sugar | 200 g | 7.05 oz |
| Brown sugar (packed) | 213 g | 7.51 oz |
| Powdered sugar | 120 g | 4.23 oz |
| Butter | 227 g | 8.0 oz |
| Cocoa powder | 85 g | 3.0 oz |
| Rolled oats | 90 g | 3.17 oz |
| Honey | 340 g | 12.0 oz |
Flour is the worst offender: scooped straight from the bag it can hit 150 g, 25% over the spooned-and-leveled 120 g that most American recipes assume. King Arthur Baking and America's Test Kitchen both publish 120 g/cup as the reference.
Smaller measures
| Measure | US fl oz | Milliliters |
|---|---|---|
| 1 teaspoon | 1/6 | 4.929 mL |
| 1 tablespoon | 1/2 | 14.787 mL |
| 1/4 cup | 2 | 59.15 mL |
| 1/3 cup | 2.67 | 78.86 mL |
| 1/2 cup | 4 | 118.29 mL |
| 1 pint | 16 | 473.18 mL |
| 1 quart | 32 | 946.35 mL |
An imperial fluid ounce is 28.413 mL against the US 29.574 mL — about 4% smaller, in the opposite direction to the gallon.
Why bakers weigh
Volume measurement of dry goods varies by up to 20% depending on how the cup is filled, how settled the flour is and the humidity. Weight does not. Professional bakeries work in grams and express recipes as baker's percentages against flour weight. A €15 kitchen scale removes the largest single source of inconsistency in home baking.
Key takeaways
- 1 US cup = 8 fl oz = 236.588 mL, by volume only
- Weight per cup depends entirely on the ingredient
- US, metric and UK cups differ by up to 20% — check the recipe's origin
- Weigh flour at 120 g/cup rather than scooping