US gallons to US quarts (gal to qt)

One US gallon is exactly 4 US quarts. 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: 2 gal x 4 = 8 qt.

Going the other way, one US quart is 0.25 US gallons.

To convert without a calculator, multiply by 4. Rounding that to 4 is within 0% for most purposes.

Four quarts to a gallon, which is the step most often needed when scaling paint, oil or a batch recipe up from the container size it is sold in.

Precision is worth matching to the input. A measurement given as 0.5 gal carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.