To convert cups to fluid ounces (cup to fl oz), multiply by 8. 1 cup equals 8 fl oz, about 67% of a soft-drink can.
| cups | fluid ounces |
|---|---|
| 1 cup | 8 fl oz |
| 2 cups | 16 fl oz |
| 5 cups | 40 fl oz |
| 10 cups | 80 fl oz |
| 25 cups | 200 fl oz |
| 50 cups | 400 fl oz |
| 100 cups | 800 fl oz |
| 250 cups | 2,000 fl oz |
| 500 cups | 4,000 fl oz |
| 1000 cups | 8,000 fl oz |
The factor is 8.00000, which is derived rather than defined, so any decimal you see has been rounded somewhere.
For mental arithmetic the factor is close enough to 8 to use directly: multiply cups by 8 and the answer is right to within a rounding error.
The reverse factor is 0.125, so one fluid ounce is that many cups. Two decimal places is plenty for most purposes, and three is more than a tape measure can justify.
To anchor the scale: 1 cup is about 8 fl oz.