Pool Filter Size Calculator
Changes with the filter type.
Minimum filter area
160 sq ft
At 60 GPM, a cartridge filter needs at least 160 sq ft of filter area. Smallest common size: 200 sq ft.
- Suggested size
- 200 sq ft
- Design rate
- 0.38 gpm/sq ft
- Actual rate at that size
- 0.3 gpm/sq ft
How it's calculated
| Filter | Design rate used | Maximum |
|---|---|---|
| Sand | 15 gpm/sq ft | 20 gpm/sq ft |
| Cartridge | 0.375 gpm/sq ft | 0.375 gpm/sq ft |
| DE | 2 gpm/sq ft | 2 gpm/sq ft |
Maximum design filtration rates for residential pools, ANSI/APSP/ICC-5 (Residential Inground Swimming Pools); the same cartridge and DE limits appear in the CDC Model Aquatic Health Code. Sand is shown at a conservative 15 gpm/sq ft design rate (20 is the maximum). The suggested size is the smallest common model that meets the minimum area: sand filters are sold by tank diameter, cartridge and DE filters by filter area.
Worked example
A pump delivering 60 GPM with a cartridge filter:
- Minimum area: 60 ÷ 0.375 = 160 sq ft.
- Smallest common cartridge at or above that: 200 sq ft.
- Actual rate: 60 ÷ 200 = 0.3 gpm/sq ft, inside the limit.
The same flow through sand at 15 gpm/sq ft needs 4 sq ft. A 26" tank has 3.69 sq ft (too small), a 30" tank has 4.91 sq ft, so choose 30".
Choosing a filter comfortably above the minimum lowers the filtration rate, which stretches the time between cleanings and keeps pressure down. The extra cost is usually small.
Smallest common filter by flow rate
| Flow | Cartridge | Sand tank | DE |
|---|---|---|---|
| 30 GPM | 100 sq ft | 21" | 36 sq ft |
| 40 GPM | 150 sq ft | 24" | 36 sq ft |
| 50 GPM | 150 sq ft | 26" | 36 sq ft |
| 60 GPM | 200 sq ft | 30" | 36 sq ft |
| 80 GPM | 250 sq ft | 36" | 48 sq ft |
| 100 GPM | 300 sq ft | 36" | 60 sq ft |
Common residential filter sizes sold in the US (sand: tank diameter in inches; cartridge and DE: filter area in sq ft). "—" means larger than common residential sizes.
Sand tank sizes
| Tank | Area | Max flow at 15 gpm/sq ft |
|---|---|---|
| 19" | 1.97 sq ft | 29.5 GPM |
| 21" | 2.41 sq ft | 36.1 GPM |
| 22" | 2.64 sq ft | 39.6 GPM |
| 24" | 3.14 sq ft | 47.1 GPM |
| 26" | 3.69 sq ft | 55.3 GPM |
| 30" | 4.91 sq ft | 73.6 GPM |
| 36" | 7.07 sq ft | 106 GPM |
Frequently asked questions
What size filter do I need for a 20,000 gallon pool?
Start from the pump flow. An 8-hour turnover of 20,000 gallons is about 42 GPM, which needs a 150 sq ft cartridge, a 24" sand tank or a 36 sq ft DE filter at the rates on this page. Size for your pump's actual flow if it is higher.
Can a pool filter be too big?
No. A larger filter runs at a lower filtration rate, which usually means better filtering, lower pressure and longer intervals between cleanings. The only downsides are purchase price and space.
Which is better: sand, cartridge or DE?
Sand is cheapest and simplest but filters the coarsest particles. Cartridge filters catch finer particles, need no backwashing and save water. DE filters the finest but needs DE powder recharged after each backwash. Any of them works if it is sized correctly.
What happens if my filter is too small?
Water is pushed through the media faster than it is designed for. Pressure climbs quickly, the filter needs frequent cleaning, dirt can be forced through, and the pump moves less water than expected.
How do I find my pump flow rate?
Read it from the pump curve at your system head, use the pump size calculator, or for variable-speed pumps read the GPM on the display if it shows one. The turnover rate calculator can also work out flow from a measured turnover.
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