Understand the relationship
Visual explanation
Measuring cups often mark 2, 4, 6, and 8 fluid ounces along the side. The 8-fluid-ounce line represents one full US customary cup.
A fluid ounce tells how much space a liquid occupies. A weight ounce tells how heavy something is. Eight fluid ounces of different liquids occupy the same volume but may not weigh the same.
Calculate it
The formula
US fluid ounces = US cups × 8Instant converter
Convert while you learn
1 US customary cup equals
US fluid ounces
Calculated from the canonical unit dataset.
1 × 236.5882365 mL ÷ 29.5735295625 mL
Follow the reasoning
Worked examples
Convert 3 cups to fluid ounces.
3 × 8 = 243 cups = 24 US fl oz
Convert ⅔ cup to fluid ounces.
(2 ÷ 3) × 8 = 5⅓⅔ cup = 5⅓ US fl oz
Convert 20 fluid ounces to cups.
20 ÷ 8 = 2.520 US fl oz = 2½ cups
Quick lookup
US customary cup to US fluid ounces chart
| US customary cups | US fluid ounces |
|---|---|
| 0.125 | 1 |
| 0.25 | 2 |
| 0.3333333333 | 2.6666666664 |
| 0.5 | 4 |
| 0.75 | 6 |
| 1 | 8 |
| 2 | 16 |
Values are generated from the same canonical constants used by the converter. Decimal display may be rounded.
Common mistake
Check the unit and direction
Do not use this rule to convert a recipe’s dry-weight ounces into cups. Flour, sugar, and butter have different densities, so weight-to-volume conversion depends on the ingredient.
Remember it
On a standard US liquid measuring cup, the top line is commonly 8 fluid ounces—the same as 1 cup.
Quick practice
How many fluid ounces are in 2¼ cups?
18 US fl oz, because 2.25 × 8 = 18.
Accuracy note: Core U.S. liquid relationships and the 231-cubic-inch gallon were checked against NIST Handbook 44 (2026), Appendix C. SI definitions were checked against NIST SI Units—Volume. Imperial values were checked against the UK Weights and Measures Act 1985. Values were last checked on . Review the source list.