The power required to move water with a pump is called the water horsepower and can be computed by the following equation:
Brake horsepower is the actual horsepower needed to operate the pump and accounts for inefficiencies in the pump. Brake horsepower can be obtained by dividing water horsepower by the pump efficiency, expressed as a decimal:
Combining these two equations gives a convenient equation for brake horsepower:
Note that this does not include power losses within the motor or engine driving the pump.