gpm
ft
HP

Formula

Water Horsepower :
WHP = QH/3960

Flow Rate or Discharge :
Q =3960 WHP/H

Total Head / Total Dynamic Head (TDH) :
It is defined as the total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe. Sum of discharge head, suction lift, and friction loss.

H = 3960 WHP/Q

Where,
WHP = Water Horsepower,
Q = Flow Rate or Discharge,
H = Total Head.