How many gallons per foot in 2.5 inch pipe?

The equation for a cylinder is pi*r2*h. pi=3.141593, r=2.5in/2=1.25in, h=12in.

This results in a volume of 565.486678in3.

To convert to gallons divide by 231(in3/US gallon).

565.486678in3/231= 2.447994 US gallons per foot.

This equation assumes that the inner diameter of the pipe is 2.5 inches.