Pump & Filter Sizing
Turn your pool over in ~8 hours. Get the flow your pump needs and the minimum filter size.
Pump & filter sizing (turnover method)
A residential pool should turn its entire volume over in about 8 hours. That sets the flow your pump must deliver and the minimum filter area.
Required flow & filter size
| Filter type | Minimum size for 42 GPM |
|---|---|
| Cartridge | 111 sq ft of media |
| D.E. (diatomaceous earth) | 20.8 sq ft grid area |
| Sand | 2.8 sq ft of bed area |
Show the math
Flow (GPM) = volume ÷ (turnover hours × 60) = 20,000 ÷ (8 × 60) = 42 GPM.
Cartridge area = flow ÷ 0.375 GPM/sq ft = 111 sq ft. Oversizing the filter (and matching pump to filter) means longer runs between cleanings.
Guideline only. Real pump selection also depends on plumbing size, head loss, and whether you run a variable-speed pump (recommended, and often required by code). Never exceed your filter’s or plumbing’s rated maximum flow.
What is turnover?
Turnover is the time it takes to circulate your entire pool volume through the filter once. Residential pools generally target one turnover in 8 hours; the required flow rate follows directly from your volume.
Sizing the filter
A common mistake is matching a big pump to a small filter. Filters have a rated maximum flow; exceeding it channels water through the media and cleans poorly. Cartridge filters are sized at roughly 0.375 GPM per square foot of media — bigger is better, since more area means longer runs between cleanings. Pair this with the cartridge finder to identify replacement elements.
A volume figure is the only input you need to start.