This is the volume of a cylinder; pipe capacity is usually amount of flow per unit of time under given conditions of internal roughness, and viscosity of the flowing fluid with a given pressure loss per length unit.
Q = DELTA PRESSURE * PI*( DIAMETER TO FOURTH POWER)/ (128 * VISCOSITY* LENGTH)
VISCOSITY OFWATER IS ABOUT 2X1O TO -5 POWER LB SECOND/FT SQUARED
NOTE PRESSURE MUST BE BELOW AMOUNT THAT RUPTURES THE PIPE.