Convert cups to gallons (cup to gal)

One US cup is exactly 0.0625 US gallons. That ratio belongs to the customary system itself and is much older than any link to metric: the 1959 international yard and pound agreement later fixed the yard and the pound against the meter and the kilogram, but it left the ratios between customary units (feet to the yard, ounces to the pound, cups to the gallon) exactly as they were.

Worked through: 8 cup x 0.0625 = 0.5 gal.

Going the other way, one US gallon is 16 US cups.

To convert without a calculator, multiply by 0.0625. Rounding that to 0.063 is within 0.8% for most purposes.

Sixteen cups to a US gallon. The conversion comes up in batch cooking and in mixing anything by the gallon, where a recipe written in cups has to be scaled to a container quoted in gallons.

Precision is worth matching to the input. A measurement given as 1 cup carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.