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Pool filter size calculator
A sand filter is sized by its surface area. This uses 20 GPM per square foot, which matches the design flow listed for common residential filters.
Tank size and flow
| Tank | Area | Flow at 20 GPM/sq ft |
|---|---|---|
| 16 in | 1.4 sq ft | 28 GPM |
| 18 in | 1.77 sq ft | 35 GPM |
| 21 in | 2.41 sq ft | 48 GPM |
| 24 in | 3.14 sq ft | 63 GPM |
| 30 in | 4.91 sq ft | 98 GPM |
Check your filter's own rating: it may differ from this. The CDC's model code limits some shallow-bed filters to 12 GPM per square foot, which is one reason not to buy at the edge of the range.