How many gallons of water in a 12 inch pipe 13 feet long?

The pipe is a cylinder, with diameter = 30 inches = 1 foot, and height (length) = 25 feet.

Volume of a cylinder = pi R2 L

Volume = pi x (1/2)2 x 25 = (25/4 pi) cubic feet

1 cubic foot = 7.4805 gallons

Volume = (7.4805) x (6.25 pi) = 146.88 gallons(rounded)