Pump Horsepower Calculator
Estimate hydraulic pump power, required motor input, standard horsepower size, daily energy and operating cost from flow, head and efficiency.
Default project preview
1.5 hp
Hydraulic power
0.6 kW
Pump input power
0.93 kW
Reserved power
1.07 kW
Daily electricity
3.71 kWh
Calculator
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Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Design flow
Enter this project assumption in gal/min. The current imperial default is 40 gal/min.
Total dynamic head
Enter this project assumption in ft. The current imperial default is 80 ft.
Overall pump efficiency
Enter this project assumption in %. The current imperial default is 65 %. Minimum: 1. Maximum: 100.
Motor reserve
Enter this project assumption in %. The current imperial default is 15 %. Minimum: 0. Maximum: 50.
Operating time
Enter this project assumption in hours/day. The current imperial default is 4 hours/day. Minimum: 0. Maximum: 24.
Electricity price
Enter this project assumption in per kWh. The current imperial default is 0.18 per kWh. Minimum: 0.
How to read the outputs
Hydraulic power
power delivered to water. Default preview: 0.6 kW.
Pump input power
65% efficiency. Default preview: 0.93 kW.
Reserved power
15% motor reserve. Default preview: 1.07 kW.
Daily electricity
4 operating hours. Default preview: 3.71 kWh.
Daily energy cost
entered tariff. Default preview: $0.67.
Flow conversion
24.4 m head. Default preview: 151.4 L/min.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Hydraulic power = density × gravity × flow × head. Input power divides by efficiency. Motor reserve is applied before rounding up to a common horsepower size.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Estimate hydraulic and input power from flow, total dynamic head and assumed efficiency.
Calculation steps
- 1Enter the actual project dimensions or operating values.
- 2Apply the calculator formula using consistent units.
- 3Review the unrounded result and the editable allowance.
- 4Round only to the product, stock length or equipment increment actually purchased.
Worked numerical example
Moving 50 gpm against 100 ft of head requires about 1.26 hydraulic hp; at 65% efficiency input is about 1.94 hp.
Purchasing and rounding
Use the calculated input horsepower as a hydraulic sizing checkpoint, then select a pump from a manufacturer curve at the required flow and total dynamic head. Do not simply buy the next motor horsepower: the operating point, efficiency, impeller diameter, service factor and motor rating must all be compatible.
Interpret the result
The hydraulic horsepower is the power transferred to the water; the higher input horsepower accounts for efficiency. A pump with the calculated motor size can still be wrong if its curve does not intersect the required flow and head at an acceptable efficiency.
Page-specific assumptions
- Inputs describe one consistent project condition.
- Entered yields and efficiencies match the selected product or equipment.
- Site-specific code and engineering requirements are checked separately.
Common mistakes
- Mixing imperial and metric inputs.
- Using nominal dimensions where actual coverage controls.
- Rounding intermediate values too early.
- Treating a quantity estimate as design approval.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
FAQ
Pump Horsepower Calculator questions
Why is motor power higher than hydraulic power?+
Pump and motor losses mean more input power is required than the useful power delivered to the water.
Can horsepower alone select a pump?+
No. The pump curve must meet both design flow and total dynamic head with acceptable efficiency and suction conditions.
What is total dynamic head?+
It combines static lift, required discharge pressure and friction losses at the design flow.