Engineering CalculationPump Power Calculator - kW, Motor Rating and NPSH
Find the hydraulic power, shaft power and motor rating of a pump from its flow, head and efficiency, and check NPSH.
Open the calculator →Formula
Pshaft (kW) = ρ × g × Q × H / (1000 × η)
ρ = density (kg/m³), Q = flow (m³/s), H = total head (m), η = pump efficiency
Worked example
Water, 100 m³/h, 40 m head, pump efficiency 70 %
Hydraulic power = 1000 × 9.81 × 0.0278 × 40 / 1000 = 10.90 kW; shaft power = 15.57 kW
Where engineers use it
- Cooling water, process and fire pumps
- Checking an installed motor for a new duty
- Energy audits of pumping systems
How to use
- Click Open the calculator. It runs free in your browser, on desktop or phone.
- Enter your values. Units and typical ranges are shown next to each input.
- Read the result and the step-by-step working, then print or add it to your Project BOQ.
Questions
Does it size the motor?
Yes, it adds a margin over shaft power and suggests the next standard motor rating.