Estimate total dynamic head from elevation, pipe friction, and fitting losses, then calculate
hydraulic power, pump shaft power, and estimated electrical input.
Already know the total dynamic head?
For a direct flow-and-head power calculation, enter the operating point and read hydraulic and shaft power; the head-loss build-up is optional.
Inputs
Edit directly if project-specific data are available. Typical water-service values are generally about 80–150.
Static head—
Friction loss—
Minor losses—
Pipe velocity—
Total dynamic head—
Pipe friction is estimated with Hazen–Williams. Minor losses use hm = ΣK·v2/(2g). The calculated head includes elevation, straight-pipe friction and entered minor losses; add pressure or equipment head separately when required.
Calculated-head mode is intended for water-like fluids in turbulent flow. Use Darcy–Weisbach for non-water fluids, viscosity-sensitive applications, or detailed design.
1000 kg/m3 = water at room temperature
Typical centrifugal pumps run 60–85% efficiency
Used only to estimate electrical input power.
Results
Hydraulic power—
Shaft (brake) power—
Estimated motor electrical input—
Pₛ = ρ · g · Q · H Pś = Pₛ / ηpump Pelec = Pś / ηmotor
Worked Example
A pump lifts water from a lower reservoir to an elevated tank, 25 m higher,
at a flow rate of 40 m3/h. Pump efficiency is 70%.
Convert flow to SI base units: Q = 40 / 3600 = 0.0111 m3/s
Pś ≈ 3.89 kW. Select the motor from the pump manufacturer’s maximum absorbed-power curve and the required service margin; a 5.5 kW standard motor may be appropriate for this simplified example. Confirm the motor rating against the full pump curve, service factor, starting method and applicable standard.
Frequently Asked Questions
Hydraulic power is transferred to the fluid. Shaft power is the mechanical input at the pump shaft and is higher because pump efficiency is below 100%.
No. Electrical input power is approximately shaft power divided by motor and drive efficiency.
Use Darcy–Weisbach for non-water fluids, laminar or transitional flow, viscosity-sensitive applications, or detailed hydraulic design.
No. The built-in head estimate includes elevation, straight-pipe Hazen–Williams friction and the entered ΣK minor losses. Add vessel pressure differences, filters, heat exchangers, control valves and other equipment head separately.
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