US fluid ounces and US cups
The US fluid ounce is 1/128 of a US gallon: exactly 29.5735295625 milliliters. Drink cans and bottles, cosmetics and US recipes use fluid ounces. It measures volume, unlike the ounce of weight.
The US customary cup is half a US pint: 8 US fluid ounces, exactly 236.5882365 milliliters. American recipes measure flour, sugar, milk and water in cups. US nutrition labels use a rounded legal cup of 240 mL.
Worked example
Convert 12 fl oz: 12 × 0.125 = 1.5, so 12 US fluid ounces is 1.5 US cups. Likewise 20 fl oz = 2.5 cup.
Estimating in your head
Divide by 8 for a quick figure; it is off by about 0%. For 12 fl oz that gives 1.5 cup, against 1.5 exactly.
Going the other way
To convert US cups to US fluid ounces, divide by 0.125 (or multiply by 8). The swap button between the boxes opens that page.
How this works
cup = fl oz × 0.125
1 fl oz = 0.0000295735295625 m³ and 1 cup = 0.0002365882365 m³, both by definition, so the factor is their ratio: 0.125 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many US cups are in a US fluid ounce?
1 US fluid ounce = 0.125 US cups, exactly. The value follows from the unit definitions, so it never changes.
How do I convert US fluid ounces to US cups?
Multiply by 0.125. For example, 20 fl oz × 0.125 = 2.5 cup.
What is 100 fl oz in US cups?
100 fl oz = 12.5 cup. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- NIST Handbook 44 — Appendix C, General tables of units of measurement
- Wikipedia — United States customary units
Reviewed Oct 17, 2026 · test vectors fixtures/units/volume/oz-to-cups/