Pump Sizing

Hydraulic and shaft horsepower from flow, total dynamic head, and pump efficiency.

Run the calculator

Example

You enter

Flow (gpm) 100
Total dynamic head (ft) 80
Pump efficiency (0-1) 0.65
Fluid specific gravity 1

You get

Hydraulic hp 2.02
Shaft hp 3.108

Checked against published worked examples from: Pennsylvania Department of Environmental Protection, Bureau of Safe Drinking Water.

Details, formula, and sources

Formula or tableHydraulic HP = (GPM × TDH × specific_gravity) / 3960; shaft (brake) HP = hydraulic HP / pump_efficiency. Total dynamic head (TDH) is supplied by the user.

Source and editionHydraulic Institute by name; Hazen-Williams (AWWA M11 5th ed.) for friction term.

Free accessHydraulic Institute standards licensed; principles free in published engineering texts and university OCW.

What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

API field namesflow_gpm, total_dynamic_head_ft, efficiency, fluid_specific_gravity, hydraulic_hp, shaft_hp

Pump efficiency 65% unless user supplies a curve pointHydraulic Institute typical for end-suction centrifugal
Water density / specific gravity 1.000 unless user supplies60 °F freshwater