Pool Pump Size Calculator
Pumps are rated in GPM (gallons per minute). What you need depends on your pool volume and how fast you want a full turnover 鈥?one complete pass of all pool water through the filter.
How the math works
- GPM = Gallons 梅 Hours 梅 60
- Example: 15,000 gallons over 8 hours = 15,000 梅 480 = 31 GPM
Buying a pump: 3 things to know
- Match the filter, not just the pool. Your filter's max flow rate must exceed your pump's output, or you'll blow media into the pool or strain the system.
- Variable-speed pumps (VSP) save real money. Running a VSP at half speed moves the same daily gallons at roughly 录鈥撯厸 the energy cost. Most states (including those following the DOE rule) now require VSPs for new installs.
- Bigger is not better. An oversized pump fights your filter, wastes energy and can strain plumbing. Size to the GPM above, then round down if between models.
Frequently asked questions
How many hours a day should I run my pool pump?
Enough to turn over the full pool volume once per day 鈥?8 hours at rated flow is the common starting point. With a variable-speed pump, longer runtimes at lower speed clean better and cost less.
What GPM pump do I need for a 15,000 gallon pool?
For an 8-hour turnover: about 31 GPM at rated flow. Because real plumbing adds resistance, many owners pick a pump rated 40鈥?0% higher than the target GPM.
Does pump HP (horsepower) matter?
HP is a proxy 鈥?flow rate (GPM) against your system's resistance is what matters. Two 1-HP pumps can deliver very different flows. Always compare pump curves, not horsepower.