Calculate fluid ounces from cups instantly, with support for US customary, metric, and imperial cup and fluid ounce standards.
C to Fluid Ounce Formula
This calculator changes cups (c) into fluid ounces (fl oz) and back. The standard conversion for US cooking measurements is:
fl oz = c * 8
To go the other way:
c = fl oz / 8
When you change the cup standard or the fluid ounce system, the factor of 8 is replaced by the ratio of their volumes in milliliters:
fl oz = c * (Vc / Vo)
- fl oz = volume in fluid ounces
- c = volume in cups
- Vc = milliliters in one cup of the chosen standard
- Vo = milliliters in one fluid ounce of the chosen system
The "Cups to fluid ounces" mode multiplies your cup value by the conversion factor to give fluid ounces. The "Fluid ounces to cups" mode divides instead. The optional measurement standards control the two volumes behind the factor: the cup standard sets Vc and the fluid ounce system sets Vo. With the default US customary cup and US fluid ounce, Vc divided by Vo equals exactly 8, which is why 1 cup is 8 fluid ounces.
Cup and Fluid Ounce Standards
Different regions define the cup and the fluid ounce differently. The factor below is how many fluid ounces are in one cup for each pairing. Use the US customary row for everyday American recipes.
| Cup standard | Cup volume | Ounce system | Fl oz per cup |
|---|---|---|---|
| US customary | 236.59 mL | US | 8.0000 |
| US legal | 240 mL | US | 8.1154 |
| Metric | 250 mL | US | 8.4535 |
| Imperial | 284.13 mL | Imperial | 10.0000 |
The table below shows common cup amounts converted with the standard US factor of 8.
| Cups | Fluid ounces |
|---|---|
| 1/4 cup | 2 fl oz |
| 1/2 cup | 4 fl oz |
| 1 cup | 8 fl oz |
| 2 cups | 16 fl oz |
| 4 cups | 32 fl oz |
Example Problems
Example 1: Convert 3 cups to fluid ounces using US measurements. Multiply by 8: 3 * 8 = 24 fl oz.
Example 2: A recipe lists 20 fluid ounces and you want cups. Divide by 8: 20 / 8 = 2.5 cups.
Frequently Asked Questions
How many fluid ounces are in a cup? One US customary cup holds 8 US fluid ounces. This is a volume measurement, so it applies to liquids like water, milk, and oil regardless of weight.
Is a fluid ounce the same as an ounce? No. A fluid ounce measures volume, while an ounce measures weight. They only match for water and other liquids with a density close to water, so 8 fluid ounces of water weighs about 8 ounces, but 8 fluid ounces of honey weighs more.
Why does my result change when I pick a different cup standard? A US customary cup is 236.59 mL, but a metric cup is 250 mL and a UK imperial cup is 284.13 mL. Larger cups hold more, so they convert to more fluid ounces. Pick the standard that matches the recipe or source you are working from.
