What is hydraulic power?

Hydraulic power (also called water power or fluid power) is the useful power transferred from the pump to the fluid. It equals ρ × g × Q × H, where ρ is fluid density, g is gravitational acceleration, Q is flow rate, and H is differential head.

Shaft power is the mechanical power that must be supplied to the pump shaft by the motor. It is always higher than hydraulic power because real pumps have losses. Shaft power = Hydraulic power / pump efficiency.

What pump efficiency should I use?

Typical centrifugal pumps have efficiencies between 60% and 85%. High-efficiency models can reach 90%. If you do not know the efficiency, use 70–75% as a conservative estimate. Always check the pump curve from the manufacturer for the best operating point.

What is "head" in pump calculations?

Head is the energy added to the fluid per unit weight, expressed as a height of fluid column (meters or feet). It combines static pressure difference, elevation change, and velocity head. For most system designs, total head is calculated from the system resistance curve.

How do I convert between metric and imperial results?

1 kW = 1.341 hp and 1 hp = 0.7457 kW. This calculator shows both automatically, so you can read the result in whichever unit your motor nameplate or spec sheet uses.

Pump Power Calculator

Name: Pump Power Calculator
Availability: InStock
Author: Nham Vu

Enter flow rate, fluid head, density, and pump efficiency to get hydraulic and shaft power in metric or imperial units.

Pump Inputs

Unit System

Flow Rate (m³/s)

Differential Head (m)

Fluid Density (kg/m³)

Pump Efficiency 75%

1% 100%

Enter pump parameters and click Calculate Power.

Common Fluid Densities

Fluid	kg/m³	lb/ft³
Fresh Water (15°C)	999	62.4
Seawater (15°C)	1025	64.0
Light Oil	850	53.1
Diesel Fuel	835	52.1

Summary

Enter flow rate, fluid head, density, and pump efficiency to get hydraulic and shaft power in metric or imperial units.

How it works

Select your preferred unit system (SI or Imperial).
Enter the volumetric flow rate (m³/s or GPM).
Enter the total differential head across the pump (m or ft).
Enter the fluid density (kg/m³ or lb/ft³) — water defaults are pre-filled.
Set pump efficiency as a percentage (0–100).
The tool computes hydraulic power (P_hyd = ρ × g × Q × H) and shaft power (P_shaft = P_hyd / η) instantly.

Use cases

Size electric motors for industrial centrifugal pumps.
Calculate energy consumption in water distribution systems.
Verify pump selection for irrigation and agricultural systems.
Determine shaft power for oil and chemical process pumps.
Compare hydraulic power across different operating points.
Estimate energy cost of pumping operations.

Frequently Asked Questions

Last updated: 2026-07-24 · Reviewed by Nham Vu