Work out the hydraulic and motor power a water pump needs from the flow it must deliver and the total head — static lift plus friction — it has to overcome.
Indicative hydraulic power only. Pump selection uses the manufacturer’s pump curve at the duty point, NPSH, motor margin and the system curve — confirm against real data.
traqR keeps pump and plumbing jobs, specs and service records together so the duty you size is the pump you install and invoice.
Start free trialTotal head is the static lift plus friction losses in the pipework and any residual pressure needed at the outlet.
Hydraulic power in kW is flow (L/s) × total head (m) × 9.81 ÷ 1000 — the useful power delivered to the water.
The shaft (motor) power is the hydraulic power divided by pump efficiency. Motor selection then adds margin above that.
Work out the flow you need and the total head — static lift plus friction and residual pressure. Hydraulic power (kW) is flow in L/s times head in metres times 9.81 divided by 1,000, and the motor power is that divided by pump efficiency. For 1.5 L/s at 28 m head and 60% efficiency, that’s about 0.41 kW hydraulic and 0.69 kW at the shaft.
Total head is everything the pump must work against: the static height it lifts the water, the friction losses in pipes and fittings, and any pressure required at the delivery point. It’s expressed in metres, where 1 m is about 9.81 kPa.
Real pumps aren’t 100% efficient, and the operating point can shift along the pump curve. Dividing by efficiency gives the shaft power, and a margin is added when selecting the motor so it isn’t overloaded.
It gives an indicative power. Actual selection matches the duty point (flow and head) to the manufacturer’s pump curve, checks NPSH to avoid cavitation, and considers the system curve — best done with real pump data.
This calculator gives indicative hydraulic and shaft power only. Pump selection must use manufacturer pump curves at the duty point, NPSH and motor margins, and plumbing must comply with AS/NZS 3500 and be carried out by a licensed plumber.
traqR keeps pump and plumbing jobs, specs and records together so the duty you size is the pump you invoice. Try it free for 14 days.