To convert cups to quarts (cup to qt), multiply by 0.25. 1 cup equals 0.25 qt, about 67% of a soft-drink can.
| cups | quarts |
|---|---|
| 1 cup | 0.25 qt |
| 2 cups | 0.5 qt |
| 5 cups | 1.25 qt |
| 10 cups | 2.5 qt |
| 25 cups | 6.25 qt |
| 50 cups | 12.5 qt |
| 100 cups | 25 qt |
| 250 cups | 62.5 qt |
| 500 cups | 125 qt |
| 1000 cups | 250 qt |
The factor is 0.250000, which is derived rather than defined, so any decimal you see has been rounded somewhere.
For mental arithmetic the factor is close enough to 0.25 to use directly: multiply cups by 0.25 and the answer is right to within a rounding error.
Going the other way, one quart is 4 cup, which is usually the easier direction to work in. Because the forward factor is small, watch the decimal place rather than the digits: a factor-of-ten slip is the common error, not a rounding one.
To anchor the scale: 5 cups is about 1.25 qt.