Assuming you're talking inner diameter (ID) of the pipe some basic math will answer this question.
Volume of a cylinder = pi * radius^2 * length So for us, pi *.25*.25*12 = 2.35619449 cubic inches = 1.30559695 US fluid ounces. So a better question would be how many oz per foot.
0.255 gallons per foot of pipe. A 10 ft long pipe that size holds 2.55 gallons.
2.61153 gallons.
2000 Gallons
0.6528 gallon per foot (rounded)
3,231.5844
One foot of 3 inch pipe will hold approximately 0.625 gallons of water.
36.7 US gallons.
36.7 US gallons.
15228.5 US gallons 12680.4 Imperial gallons when it is filled to 4 and a half feet.
For a 1-inch line, there are approximately 0.01866 gallons per foot.
1.47
A 12 inch diameter round pipe will hold 4.89 UK gallons or 5.88 US gallons per foot.