Pump size calculator
You need roughly 31 GPM to turn the pool over in 8 hours. Match that against the pump's flow curve at your plumbing's head loss — not the number on the box.
Treat this as a starting dose: add less than the full amount when unsure, circulate for a few hours, retest, repeat. Always follow your product's label.
The right pump isn't the biggest one — it's the one sized to move your pool's water in a reasonable time without overpowering your filter or plumbing. The calculator above turns your pool volume and turnover goal into a target flow rate; here's how to use it.
What it calculates
Enter your pool volume and desired turnover time (how long to cycle all the water through the filter), and the tool returns the flow rate in gallons per minute your pump needs to hit. That flow target — not horsepower — is the number that matters. Bigger isn't better: an oversized pump wastes energy, can exceed your filter's rated flow, and can create problems in your plumbing.
Check it against your filter and plumbing
A pump has to match the rest of the system. Confirm the target flow doesn't exceed your filter's maximum flow rating, and that your plumbing size can carry it without excessive resistance. If the numbers push past your filter's limit, the fix is usually a right-sized variable-speed pump run at an efficient speed, not a bigger single-speed unit forcing more water than the filter can take.
Variable speed is usually the answer
For most pools that run several hours a day, a variable-speed pump is the efficient choice — it filters on a quiet, cheap low speed and ramps up only for vacuuming or a heater. Use the flow target from this tool to pick a pump that meets your needs efficiently, then confirm against the pump's own performance curve or a pro's advice. Our best-pumps guide covers specific models once you know your target flow.
Frequently asked questions
What size pool pump do I need?
You need a pump that can move enough water for your pool, filter, plumbing, and features without overpowering the system. Pool gallons, target turnover, pipe size, filter rating, and equipment needs matter more than horsepower alone.
Is a bigger pool pump better?
Not automatically. An oversized pump can waste electricity, stress plumbing, push too much flow through the filter, and make the system louder.
Should I buy a variable-speed pool pump?
Variable-speed pumps are often worth comparing because they can run slower for filtration and faster only when needed. ENERGY STAR says variable-speed and multi-speed pumps can cut energy costs and run quieter.
Can a calculator replace a pool professional?
No. A calculator can narrow the choice, but plumbing, filter rating, equipment pad layout, local code, and electrical work may require a qualified installer.
What is GPM?
GPM means gallons per minute. It is the flow rate, or how much water the pump can move under a specific set of conditions.
Embed this calculator (free)
Run a pool site or blog? Drop this tool into any page — it stays free and links back here. Paste this HTML where you want it to appear.
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