A number, N_s , used to predict the performance of centrifugal and axial pumps or hydraulic turbines: for pumps, N_s = N √Q/H^3/4; for turbines, N_s = N = √P/H^5/4, where N_s is specific speed, N is the rotational speed in revolutions per minute, Q is the rate of flow in gallons per minute, H is head in feet, and P is shaft horsepower.