How is pump motor power calculated?

Hydraulic power of the pump Q·H/367 (kW; Q m³/h, H m, for water), shaft power is found by dividing this by the pump efficiency, and motor power is found by dividing the shaft power by the motor efficiency. For example, for a pump efficiency of 50 m³/h and a motor efficiency of 30 m, a motor of approximately 6.5 kW is required (7.5 kW is standard), using a pump / a motor.

P_hydraulic = Q·H/367 · P_shaft = P_hydraulic/η_pump · P_motor = P_shaft/η_motor
Example calculation: 50 m³/h, 30 m → hydraulic 50×30/367 ≈ 4.1 kW; pump → spindle 5.8 kW; motor → 6.5 kW → 7.5 kW standard motor.

Pump Motor Power (Hydraulic → Shaft / Motor)

Calculate the pump's hydraulic power, shaft power, and required motor power from the flow rate and head.

Hydraulic power
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Spindle power
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Recommended engine
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Notes: Hydraulic power (kW) = Q·H/367 (Q: m³/hr, H: m, for water) · Shaft = hydraulic/pump efficiency · Motor = shaft/motor efficiency. Cavitation/NPSH, system losses, and starting torque are also evaluated; A newer engine voltage starter (typically –15) is also recommended. This result provides preliminary information for selection.
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How is it calculated?

  1. Enter the flow rate (m³/hour) and head (m).
  2. Enter the pump and motor efficiency (%).
  3. Press Calculate; the hydraulic/shaft/motor power will be displayed.

Frequently Asked Questions

How to determine pump motor power?
First, the hydraulic power is calculated using the formula Q·H/367, then divided by the pump and motor efficiencies to find the required motor power.
Why leave a margin of error in the engine?
To account for starting, wear, and operating point drifts, the engine is typically selected with a –15 margin, up to a higher standard power.
Are NPSH/cavitation included in this calculation?
No; cavitation (NPSH), pipe friction losses, and the system curve must also be evaluated.

Related tools and services

This tool and its content are for general informational purposes only; they do not constitute a binding inspection/declaration of conformity. Definitive results will be determined through on-site inspection in accordance with relevant legislation and standards. Get a quote →