Water Horsepower Calculator
Calculate water horsepower, required pump horsepower, flow rate, total head, or pump efficiency using water flow and head with metric and US customary units.
Calculate Water Horsepower
Water Power Result
What Is a Water Horsepower Calculator?
A Water Horsepower Calculator estimates the hydraulic power transferred to water or another liquid from its flow rate and total head. Water horsepower represents useful fluid power and does not include pump or motor efficiency losses.
The calculator is useful for pump systems, irrigation, water supply, wells, industrial fluid systems, HVAC applications, and basic hydraulic engineering calculations.
In addition to water horsepower, this tool can estimate required pump horsepower, flow rate, total head, and pump efficiency.
Water Horsepower Calculator Formulas
Uses flow in US gallons per minute and head in feet.
General SI relationship for hydraulic power transferred to a moving liquid.
Estimates shaft horsepower after accounting for pump efficiency.
Calculates flow rate when water horsepower and head are known.
Calculates total liquid head from horsepower and flow.
Calculates hydraulic efficiency from output and shaft power.
Water Horsepower vs Pump Horsepower
Water Horsepower
Water horsepower is the useful hydraulic power transferred to the liquid. It is based on flow rate, head, and liquid specific gravity.
Pump Horsepower
Pump horsepower represents the mechanical input power required at the pump shaft. Because real pumps are less than 100% efficient, required pump horsepower is normally higher than water horsepower.
Why Specific Gravity Matters
Specific gravity compares the density of a liquid with the density of water. Water has a specific gravity of approximately 1 under common reference conditions.
A liquid with greater specific gravity requires more hydraulic power to move at the same volumetric flow rate and head.
For ordinary water calculations, leave the specific gravity field at 1.0.
How to Use the Water Horsepower Calculator
Select What to Calculate
Choose water horsepower, pump horsepower, flow rate, total head, or efficiency.
Enter Water Flow Rate
Enter the system flow using GPM, m³/s, m³/h, L/s, or L/min.
Enter Total Head
Enter total pump head in feet, meters, or centimeters.
Check Specific Gravity
Use 1.0 for water or enter the appropriate specific gravity for another liquid.
Calculate
Click Calculate Water Horsepower to display the answer and related hydraulic values.
Water Horsepower Calculation Example
Suppose a water system delivers 500 GPM against a total head of 100 feet. For water, use a specific gravity of approximately 1.0.
The useful hydraulic output is therefore approximately 12.63 water horsepower.
If the pump operates at 75% efficiency:
What Is Water Head?
Head is a fluid-energy measurement expressed as an equivalent height of liquid. Pump total head may include elevation changes, pressure differences, velocity effects, and losses through pipes, valves, fittings, and other components.
Because horsepower increases directly with head, a higher-head system requires more hydraulic power for the same flow rate.
Water Horsepower Calculator Applications
Estimate hydraulic power for agricultural pumping systems.
Calculate useful pump output for water distribution systems.
Evaluate power requirements for liquid transfer systems.
Estimate hydraulic horsepower from well flow and pumping head.
Support water-side pumping calculations in circulating systems.
Solve water flow, head, efficiency, and horsepower problems.
Frequently Asked Questions
For US customary units, water horsepower can be calculated as flow in GPM multiplied by head in feet and specific gravity, then divided by 3960.
Water horsepower is the useful hydraulic power transferred to a liquid by a pumping system.
No. Water horsepower is hydraulic output power, while pump horsepower represents mechanical input power. Real pump horsepower is normally higher because efficiency is below 100%.
For common engineering estimates, water is typically assigned a specific gravity of approximately 1.0.
Lower pump efficiency requires more shaft horsepower to deliver the same amount of useful hydraulic power.
Yes. Enter flow in US gallons per minute and total head in feet, then use a specific gravity of 1 for water.