Pool Pump Size Calculator

How the pool pump size calculator works

Flow rate is volume divided by time. Turn 20,000 gallons over in 8 hours and you need 42 gallons per minute, which is a modest pump on 2 inch pipe.

Filters are rated in square feet of media. Bigger filters run longer between cleanings and cost less in head pressure, so oversizing the filter is a good move even when the pump stays small.

The formula, step by step

GPM = Pool Gallons / (Turnover Hours x 60)

• Divide pool gallons by the turnover hours you want.
• Divide that result by 60 to get gallons per minute.
• Match the filter so its rated flow is at or above your GPM.
• Check the pipe: 1.5 inch handles about 45 GPM, 2 inch handles about 75 GPM.

Worked example

A 24,000 gallon pool on an 8 hour turnover.

24,000 / 8 = 3,000 gallons per hour. 3,000 / 60 = 50 GPM.

That calls for a 2 inch suction line and a cartridge filter around 320 square feet for comfortable run times.

Watch it done

This short video walks through the same job in real life, so you can match what you see on screen to what you do at the pool.

Play video

Tips before you start

A variable speed pump running low and long beats a single speed pump running high and short. Half the speed uses roughly one eighth of the power, so the same turnover costs far less on the electric bill.

Pipe size sets the ceiling. Forcing 80 GPM through 1.5 inch pipe creates noise, wasted power and early wear on the pump seal, no matter what the motor is rated for.

Pool Pump Size Calculator FAQs