Pump Horsepower Calculator
Find the hydraulic and brake horsepower of a pump.
Pump horsepower is the power needed to move fluid against a head.
How the Math Works
The Pump Horsepower Calculator uses the formula HHP = Q·H·SG ÷ 3960 to determine hydraulic horsepower. In this equation, Q represents the volumetric flow rate in gallons per minute (GPM), H is the total head in feet, and SG denotes the specific gravity of the fluid (with water as the baseline at 1.0). The constant 3960 serves as a unit conversion factor that transforms the combined units of GPM, feet, and specific gravity into horsepower. Multiplying these three values together gives the energy transferred to the fluid, and dividing by 3960 converts this to the actual mechanical power required at the pump shaft, known as brake horsepower (BHP).
Practical Applications
To use this calculation practically, first measure or obtain the flow rate (Q) in gallons per minute from your pump specifications or using a flow meter. Next, determine the total head (H) by measuring the vertical distance the fluid must be lifted plus any friction losses in the piping system. Identify the specific gravity (SG) of your fluid—water has SG=1.0, while other fluids may be heavier or lighter. Plug these values into the formula to calculate the hydraulic horsepower, then apply a pump efficiency factor (typically 0.6-0.9) to determine the actual brake horsepower required from your motor.
Day-to-Day Use
This calculation helps you choose the right size motor for your pump system, preventing costly mistakes like undersized motors that burn out or oversized motors that waste energy. Whether you're installing a new irrigation system for your garden, setting up a home aquarium filtration system, or evaluating commercial hydronic heating equipment, knowing the horsepower requirements helps you budget for electricity costs and ensures your equipment can handle the workload. It's especially valuable for DIY enthusiasts working on hydraulic projects, allowing them to make informed decisions about pump selection and system design before making expensive purchases.
Worked example
100 GPM, 50 ft, water, 70% → 1.26 hydraulic HP, 1.8 brake HP.
FAQ
Why is brake HP higher?
It includes losses, so the motor must supply more than the hydraulic power.