The pump size for a pond is dependent on several factors and can generally be determined by considering the total cubic feet of water in the pond multiplied by 7.5. A high-quality pond pump will have a performance chart listed in its specifications to help determine the flow rate, or gallons per hour, of the pump.
In order to determine the proper pump size for a pond, consider the size of the pond, water flow head pressure or how high the water is to be pumped and what type of pump is to be used: a submersible or an external.
Determine the total cubic feet of water by multiplying the average length, width and the depth of the pond. For example, if the pond is approximately 3 feet deep, 12 feet long and 8 feet wide, the cubic water volume would equal 3x12x8, or 288 cubic feet. Take the total cubic feet, 288 in this case, and multiply by 7.5, which equals 2,160 gallons of water. An accurately sized pump will circulate the water once every 2 hours. There are also online pump calculators that can determine correct pump size based on the pond's total cubic feet of water.
Consult the pump's specifications to make certain the pump size can efficiently pump the volume of water needed. This will be noted as the pump's gallon per hour capacity.