How much water is in a 20 feet of 1.25 inch pipe?

Answer 1

Volume of a cylinder = (pi) x (radius)2 x (length)

Volume of the pipe section = (pi) x (0.625)2 x (240) = 294.52 cubic inches = 1.275 gallons (rounded)

That's the volume of the pipe. We have no way to know how much water is in it,

or whether it's half-full of something else, or whether it's empty etc.