Pump Power Calculator

Sizing a pump or its motor comes down to one question: how much power does it take to move the fluid you need, as high as you need to lift it? This calculator answers it from four inputs. Enter the flow rate in cubic metres per hour, the total head in metres, the pump efficiency, and the fluid density, and it returns both the hydraulic power, the useful power delivered to the fluid, and the shaft power, the power the motor must actually supply, in kilowatts. The physics behind it is the same energy idea that governs lifting anything: the power needed is the weight of fluid moved each second multiplied by the height it is raised, which works out as the density times gravity times the flow rate times the head. Because no pump is perfect, the shaft power the motor sees is larger than the hydraulic power, and the gap is the pump's efficiency, so the calculator divides by efficiency to give the real motor demand. Two details make the result trustworthy. First, head should be the total head, the vertical lift plus the friction losses in the pipes and fittings, not just the static height, or the pump will be undersized. Second, density lets you handle fluids other than water, which is set as the default at 1,000 kilograms per cubic metre but can be changed for slurries, oils or warm water. Use it to choose a pump and motor for irrigation, water supply, drainage, a transfer system or a process line, to check an existing pump is not overloaded, or to estimate running power and energy cost. It is a practical tool for engineers, plumbers, irrigation designers and students. The formula and a worked example are below.

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Use total head, including friction losses, for a realistic figure. A planning estimate; confirm against the pump manufacturer's curve.