Pump Horsepower Calculator

Your details

Head-based mode uses flow rate and total head. Pressure-based mode uses flow rate and system pressure (common for hydraulic circuits).
Volume of fluid moved per minute (imperial: gallons per minute; metric: litres per second).
GPM
Total dynamic head: sum of static lift, friction losses, and velocity head the pump must overcome.
ft
Fluid density relative to water (water = 1.0). Use 0.85 for diesel, 1.2 for brine, etc.
The ratio of hydraulic power delivered to the fluid to the shaft power input (typical range: 50-90%).
%
Efficiency of the electric motor or engine driving the pump shaft. Factors in electrical-to-mechanical conversion losses.
%
Required input horsepowerSmall pump
3.741hp

Total shaft (or motor input) power required to drive the pump

Required input power2.79kW
Water horsepower (WHP)2.525
Brake horsepower (BHP)3.367
Overall wire-to-water efficiency67.5%
Water HP (ideal)2.525
Brake HP (shaft)3.367
Total input HP3.741

Water horsepower is 2.525 hp; you need 3.741 hp of motor input power.

  • Water horsepower (2.525 hp) is the theoretical minimum assuming 100% efficiency.
  • Brake horsepower (3.367 hp) is the shaft power after accounting for pump efficiency of 75%.
  • Total input power (3.741 hp) also deducts motor efficiency (90%), giving an overall wire-to-water efficiency of 67.5%.
  • Use brake horsepower to size the pump shaft coupling, and total input power to size the motor and electrical supply.

Next stepSelect a motor rated at least 10-15% above the total input power figure to allow for starting inrush, variable loads, and component wear over time.

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