How to Calculate Water Pump Horsepower

A pump is a basic but important mechanical device used to supply the necessary force to move fluid from one position to another at a specific flow rate (usually measured in gallons per minute). Determining the power of a water pump involves calculating its ability to provide a certain amount of energy per unit of time. This is usually done in watts or, for larger devices, in horsepower (hp), where 1 unit of horsepower is equal to 746 watts.

  1. Calculate Water Pump Horsepower Step 1.jpg
    1
    Fill the base reservoir tank with water. Before you can calculate the horsepower of a pump, you need to make sure the base reservoir is completely full.
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    2
    Empty the destination reservoir. The destination reservoir is a second tank, to which the pump transfers water from the base reservoir. Make sure it is empty and connected properly to the pump.
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    3
    Measure the head of the pump. Using a scale or ruler, measure the vertical distance between the base reservoir tank and the destination reservoir (this distance is known as the “head”). Note the distance in feet.
    • For example, say the distance between the base reservoir tank and the destination reservoir is 120 feet. Write down that amount.
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    4
    Note the specific gravity. To calculate the horsepower of a pump, you need to know the specific gravity of the fluid involved. Specific gravity is a measure of how much more or less dense a particular liquid is when compared to water. The specific gravity of almost any liquid is noted on predefined physics tables.
    • Because water is the point of comparison, the specific gravity of water is 1. Write that down, too, so that now you know both the measurement of the head and the specific gravity of the fluid involved.
  5. 5
    Switch on the pump. Turn on the device, and it will start pumping water.
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    6
    Measure the flow rate. Once your pump is working, you can measure the volumetric flow rate: the volume of water transported per unit of time. Note this rate in gallons per minute.
    • Continuing with the example above, say that your flow rate is 20 gallons per minute. Write that down alongside the vertical distance between tanks and the specific gravity.
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    7
    Calculate the horsepower of the pump. You now have all the necessary information to determine the horsepower with a basic formula, shown above.
    • In the example above, plug the measurements you have already noted into the formula to find the horsepower. Your calculations will look like this:

      The horsepower of your pump is therefore 0.607 hp.