Pump Horsepower Calculator

Pump horsepower describes the rate of work needed to move a liquid through a piping system. This calculator uses the standard U.S. customary pump equation, combining flow rate in gallons per minute, total dynamic head in feet, fluid specific gravity, and pump efficiency. The first three quantities determine hydraulic horsepower, which is the useful power transferred to the liquid. Dividing that value by decimal efficiency estimates brake horsepower, the mechanical power that must reach the pump shaft. Total dynamic head is more than the vertical lift between two points. It normally includes static elevation, pressure head, and friction losses through pipe, fittings, valves, filters, and equipment. A reliable system estimate therefore depends on a realistic head calculation at the intended operating flow. Specific gravity compares the pumped liquid's density with water. Water near ordinary temperatures has a specific gravity close to 1.0, while oils are often lower and concentrated solutions can be higher. Because a denser liquid requires more power at the same flow and head, specific gravity scales horsepower directly. Efficiency accounts for losses inside the pump and drive. If a pump transfers 80 percent of its shaft power to the fluid, its decimal efficiency is 0.80. The required shaft horsepower is consequently greater than hydraulic horsepower. Use the efficiency at the expected duty point from the manufacturer's performance curve rather than a generic peak value. Motor efficiency and service factor may require additional consideration when selecting the electrical motor, because this result describes pump shaft demand rather than electrical input. The result is a sizing estimate, not a substitute for a complete pump selection. Engineers generally choose a motor with adequate margin, then confirm that the operating point lies near the pump's best efficiency region and that net positive suction head requirements are satisfied. Fluid viscosity, temperature, solids, transient conditions, and future system changes can alter actual demand. For critical installations, compare this calculation with vendor curves and applicable design standards before purchasing equipment.