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How to Calculate HP for a Centrifugal Pump

Engineers describe centrifugal pumps by their power ratings. Power is defined as the work done per unit time. You can describe power in either watts or horsepower--one unit of horsepower (HP) is equal to 746 watts. One horsepower is also 33,000 foot pounds per minute. Put simply, if a machine lifts 33,000 pounds through one foot over a period of one minute, then the machine is working at a rate of one horsepower. You can calculate the power of a centrifugal pump in horsepower using an equation that states that power equals volumetric flow rate (V) in gallons per minute, times the total discharge head (D) measured in feet, divided by 3,960, divided by the dimensionless efficiency of the pump.

Calculator
Manufacturer pump curve

Instructions

- 1
  Obtain the proper information to make the calculation. Since you are using an equation, you need to know all the required parameters. You will need to know the values for "V" in gallons per minute (GPM), "D" in feet (ft.) and efficiency as a dimensionless value.
- 2
  Simplify the calculation. Obtain a single value by multiplying "V" times "D" with the aid of a calculator. Call this value the "numerator." Multiply 3,960 by the dimensionless efficiency of the pump to obtain a single value. Call this value the "denominator."
- 3
  Perform the calculation. To do this, divide the "numerator" by the "denominator" to obtain the power of the centrifugal pump in horsepower. Your value should correspond to the power rating of the pump that is printed on the nameplate or in the manufacturer's guide.

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