💧 Pump Horsepower Calculator
Calculate a pump’s hydraulic and brake horsepower from flow rate, head, and efficiency.
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gpm
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ft
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Pump Horsepower
Water horsepower (WHP) is the theoretical power needed to move fluid against a given head, calculated as WHP = (Q × H × SG) ÷ 3960, where Q is flow rate in gallons per minute, H is total dynamic head in feet, and SG is the fluid’s specific gravity relative to water. The constant 3960 combines the standard unit conversions and water’s density.
Because no pump is perfectly efficient, the actual brake horsepower (BHP) the driving motor must supply is higher: BHP = WHP ÷ efficiency. Typical centrifugal pump efficiencies range from about 50% to 85% depending on design and operating point, so always size the motor using BHP, not WHP.
Last reviewed August 2026