Length x width x depth = Volume. 1 cubic foot (12 x 12 x 12 inches) = 7.48 gallons.
Therefore 2 cubic feet (12x 12 x 24) = 14.96 gallons.

Mikey

Pi(3.1416) x radius-squared x height of the cylinder
So a 10" diameter gas tank, 30" long would be 3.1416 x 25 x 30 = 2356.2 cu in, or about 10 gallons.

Spanky