How to size a pool pump
gallons per minute = pool gallons ÷ (turnover hours × 60)
Start from the flow, not the horsepower. A 20,000-gallon pool turned over in 8 hours needs 41.7 gpm; a 30,000-gallon pool in 6 hours needs 83.3 gpm. Then choose a pump whose curve gives that flow at your system's head, the resistance of the pipes, filter and heater, usually 40 to 60 ft of head on a home pool. The horsepower in the result is the usual range at that head, not a rule: two pumps of the same horsepower can deliver very different flows.
| Pool | 8 h turnover | Usual pump | 6 h turnover | Usual pump |
|---|---|---|---|---|
| 5,000 gal | 10.4 gpm | 0.5-0.75 hp | 13.9 gpm | 0.5-0.75 hp |
| 10,000 gal | 20.8 gpm | 0.5-0.75 hp | 27.8 gpm | 0.5-0.75 hp |
| 15,000 gal | 31.3 gpm | 0.75-1 hp | 41.7 gpm | 0.75-1 hp |
| 20,000 gal | 41.7 gpm | 0.75-1 hp | 55.6 gpm | 1-1.5 hp |
| 25,000 gal | 52.1 gpm | 1-1.5 hp | 69.4 gpm | 1.5-2 hp |
| 30,000 gal | 62.5 gpm | 1.5-2 hp | 83.3 gpm | 2-2.5 hp |
| 40,000 gal | 83.3 gpm | 2-2.5 hp | 111.1 gpm | 3 hp or two pumps |
Filter and pipes have to keep up
The filter must be rated for at least the pump's flow: sand about 20 gpm per square foot, DE about 2 and cartridge about 1, so 41.7 gpm needs at least 2.1 sq ft of sand or 42 sq ft of cartridge, and most owners go one size up. Pipe speed sets the ceiling: keep suction lines under 6 ft/s and returns under 8 ft/s. 60 gpm runs at 6.1 ft/s in 2 in pipe, so a pool that needs more than about 60 gpm wants 2.5 in plumbing or two suction lines.
Since July 19, 2021, the US Department of Energy rule for dedicated-purpose pool pumps means most new inground pumps of about 1 hp and up are sold as variable-speed models. A variable-speed pump can run the same turnover longer at lower speed; power falls with the cube of speed, so half speed uses about one eighth of the power. Not sure of your gallons? The pool gallon calculator works them out, and the pool fill time calculator shows how long a refill takes at your hose flow.
Turnover, filter rates and pipe-speed limits: Hayward and Pentair sizing guides and NSPF Pool & Spa Operator basics; DOE pool pump rule: Pentair and Jandy DOE guides. Read October 23, 2026.
Frequently asked questions
How do I calculate what size pool pump I need?
Divide your pool gallons by the turnover time in minutes: gallons ÷ (hours × 60) = gallons per minute. A 20,000-gallon pool turned over in 8 hours needs 41.7 gpm. Then pick a pump whose curve delivers that flow at your system head, usually 40 to 60 ft for a home pool.
What size pump is needed for a 16x32 inground pool?
A 16x32 pool from 3 to 8 ft deep holds about 21,000 gallons, which needs about 44 gpm for an 8-hour turnover. That is usually a 0.75 to 1 hp pump, or a variable-speed pump in the 1.5 hp class run at low speed for longer.
What size pump do I need for a 10,000 gallon pool?
About 21 gpm for one turnover in 8 hours, which is a 0.5 to 0.75 hp pump on a typical above-ground or small inground system. A larger pump does not clean better; it costs more to run and can exceed what the filter is rated for.
What is the recommended pump size for a 30,000 gallon pool?
About 63 gpm for an 8-hour turnover, or 83 gpm in 6 hours. That is usually a 1.5 to 2 hp pump with 2 in plumbing. Check pipe speed: 63 gpm in 2 in pipe runs at 6.4 ft/s, right at the 6 ft/s suction limit.
Is a bigger pool pump better?
No. Flow beyond your turnover need adds electricity cost, noise and wear, and can push water through the filter faster than its rated flow. Pump energy rises with the cube of speed, which is why a variable-speed pump at half speed uses about one eighth of the power.