Pump Horsepower Calculator – Calculate Required Pump Power

Size your pump correctly with our pump horsepower calculator. Enter flow rate, total head, and efficiency to find the required pump power in HP or kW.

Flow Rate (m³/s)

Total Head (m)

Pump Efficiency (%)

Fluid Density (kg/m³)

How to Use This Pump Horsepower Calculator

Enter flow rate and head

Input the volumetric flow rate in cubic meters per second and the total head (height) the pump must lift the fluid.

Specify pump efficiency

Enter the pump efficiency as a percentage. Typical centrifugal pumps range from 60-85% efficiency.

Get power requirements

The calculator shows hydraulic power, shaft power, and motor size in both horsepower and kilowatts.

Pump Power Calculation Formulas

The hydraulic power represents the theoretical minimum energy needed to move the fluid. The shaft power accounts for pump inefficiency — the actual power the motor must deliver.

Hydraulic Power: P_h = ρ × g × Q × H

Shaft Power: P_s = P_h / η

Horsepower: HP = P_s / 745.7

Where ρ is fluid density (kg/m³), g is gravity (9.81 m/s²), Q is flow rate (m³/s), H is head (m), and η is pump efficiency.

Typical Pump Efficiencies

Pump Type	Efficiency Range	Best For
Centrifugal (large)	80-90%	High flow, low viscosity
Centrifugal (small)	50-70%	General purpose
Positive Displacement	70-90%	High viscosity, precise flow
Submersible	60-80%	Deep wells, sewage
Gear Pump	60-80%	Hydraulic systems, oils

Frequently Asked Questions

What is total head in pump calculations?

Total head is the total height the pump must lift the fluid, including vertical lift, friction losses in pipes, and any pressure requirements at the outlet. It represents the total energy the pump must add to the fluid.

How do I choose a motor size?

Select a motor rated 10-25% higher than the calculated shaft power to provide a safety margin. This accounts for startup loads, voltage variations, and ensures the motor doesn't run at maximum capacity continuously.

Why does fluid density matter?

Denser fluids require more power to move. Water has a density of 1000 kg/m³. Oil might be 850 kg/m³, while sludge could be 1200 kg/m³. The calculator adjusts power requirements based on the fluid you specify.

What affects pump efficiency?

Efficiency depends on pump type, size, age, and operating point. Pumps are most efficient at their design flow rate. Running too far from the best efficiency point (BEP) wastes energy and causes premature wear.

How do I convert between HP and kW?

1 horsepower equals 745.7 watts or 0.746 kW. To convert HP to kW, multiply by 0.746. To convert kW to HP, divide by 0.746. Motor nameplates typically show both ratings.

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Pump Horsepower Calculator – Calculate Required Pump Power

How to Use This Pump Horsepower Calculator

Pump Power Calculation Formulas

Typical Pump Efficiencies

Frequently Asked Questions

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