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Gurukrupa Enterprises
Pump Calculators

Pump Power Calculator

Calculate hydraulic and shaft power required to pump water at a given flow and head.

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About this calculator

This calculator finds the shaft power a pump needs to deliver a given flow rate against a given total head, for water (density 1000 kg/m³), using the standard hydraulic power formula P = ρgQH, converted into the commonly used metric constant of 367.3.

Formula

P (kW) = (Q × H) ÷ (367.3 × η)
  • QFlow rate — m³/hr
  • HTotal dynamic head — metres
  • ηPump efficiency — 0–1
  • PShaft power — kW

Worked Example

Given: A pump moves 50 m³/hr of water against a 30m total head at 70% efficiency.

Result: P = (50 × 30) ÷ (367.3 × 0.7) = 5.83 kW shaft power.

How to Use

  1. Enter the required flow rate in m³/hr.
  2. Enter the total dynamic head (static lift plus friction and pressure losses) in metres.
  3. Enter the pump's efficiency from its performance curve, or use 65–75% as a typical centrifugal pump estimate.
  4. Click Calculate to get shaft power in kW.

Important Assumptions

  • Assumes water at standard density (1000 kg/m³); for other liquids, power scales directly with the liquid's specific gravity.
  • Uses total dynamic head, not just static lift — include friction losses for an accurate result (see the Pump Head Calculator).

Common Mistakes

  • Using static lift alone instead of total dynamic head, which understates required power.
  • Forgetting that motor input power will be higher again than pump shaft power, due to motor efficiency losses.

Frequently Asked Questions

Where does the constant 367.3 come from?

It is derived from P(kW) = ρ×g×Q×H with water density 1000 kg/m³, g = 9.81 m/s², and Q converted from m³/hr to m³/s — this simplifies to Q(m³/hr)×H(m)/367.3.

Is this the motor size I should buy?

This gives pump shaft power. Divide by motor efficiency to get electrical input power, then add a safety margin (commonly 10–15%) before selecting the motor frame size.

Does liquid density matter?

Yes — this formula assumes water. For other liquids, multiply the result by the liquid's specific gravity relative to water.

These calculators are provided for informational and estimation purposes. Results depend on the assumptions and input values used. Always verify critical engineering calculations against applicable standards, manufacturer specifications, site measurements, and qualified professional advice.