Pooldex

Pool Filter Size Calculator (Sand, Cartridge, DE)

For a pump that moves 50 gallons per minute (gpm), a cartridge filter needs at least 50 sq ft of filter area (1.0 gpm per sq ft). For the same flow, a sand filter needs at least 2.5 sq ft and a DE (diatomaceous earth) filter at least 25 sq ft.

By Aliaksandr Rusinski · Published October 7, 2026 · Formulas: methodology (last changed October 7, 2026)

Pool filter size calculator

Inputs
On the pump label or box (above-ground pumps often list GPH). Don’t know it? Use the pump size calculator. Example value.

Result for example values. Enter your own numbers.

Minimum filter area

50 sq ft4.65 m²

Cartridge (residential limit)

50 gal/min (3,000 GPH) at 1.0 gal/min per sq ft

Bigger than the minimum is fine: the filter runs longer between cleanings. The flow on the filter label must be at least your pump flow.

Sand
2.5 sq ft (20.0 gal/min/sq ft)
DE (diatomaceous earth)
25 sq ft (2.0 gal/min/sq ft)
Cartridge (residential limit)
50 sq ft (1.0 gal/min/sq ft)
Cartridge, sized for longer cycles (public-pool rate)
133 sq ft (0.38 gal/min/sq ft)

Rates: cartridge 1.0 (residential) and 0.375 (public) gal/min per sq ft from NSF/ANSI 50; sand 20 and DE 2.0 from Hayward filter ratings. Sand and DE amounts differ by model: use your filter manual.

Estimates, not guarantees. Always follow the product label. How we calculate

On this page (7 sections)

Size the filter from your pump's flow, not from the pool's gallons. Bigger than the minimum is fine. The filter then runs longer between cleanings.

Calculator: minimum filter area from pump flow

Enter your pump's flow in gpm and pick a filter type. Minimum filter area (sq ft) = pump flow ÷ the filter's design rate. With the example of 50 gpm and a cartridge filter, that is 50 sq ft (4.65 m²).

Don't know your pump's flow? Find it from your gallons and turnover time with the pool pump size calculator, or read it from a flow meter. Your filter needs to handle the pump's real flow, so if you plan a bigger pump, size the filter for the bigger pump.

Filter rates by type

Each filter type has a limit on how much water can pass through each square foot. At 50 gpm, the minimum areas are:

  • Sand: 2.5 sq ft, at 20 gpm per sq ft.
  • DE (diatomaceous earth): 25 sq ft, at 2.0 gpm per sq ft.
  • Cartridge, residential limit: 50 sq ft, at 1.0 gpm per sq ft.
  • Cartridge, sized for longer cycles: 133 sq ft, at 0.375 gpm per sq ft (the public-pool limit).

Where the rates come from:

  • The cartridge limits are in the filter standard NSF/ANSI/CAN 50, Table 6.4: 1 gpm per sq ft for a surface-type cartridge (the usual pleated kind) on a residential pool or spa, and 0.375 gpm per sq ft for a public one. We read them in a 2025 NSF committee ballot that quotes the table.
  • The sand and DE rates are typical ratings worked out from Hayward's published specs, not a code limit. Hayward's 24-inch sand filter (S244T2) has 3.14 sq ft of area and a public design flow of 62 gpm. Its 48 sq ft DE filter (DE4820) has a public design flow of 96 gpm.

Your own filter's label or manual gives its rated flow. That label value is the one that counts.

How much sand or DE your filter takes

The amount of sand or DE depends on the tank and grid design, so it differs from model to model. We don't publish a table by tank size, because a wrong table could mean a wrong amount. Use the number printed on your filter's label or in its manual. Two examples from Hayward's spec pages:

  • Hayward ProSeries 24-inch sand filter (S244T2): 300 lb of sand. Hayward recommends #20 silica pool filter sand for its sand filters.
  • Hayward ProGrid 48 sq ft DE filter (DE4820): 6 lb of DE, added again after each backwash.

To count bags, divide the pounds your manual lists by the weight printed on the bag and round up. For DE, go by weight, not by eye: DE is light and fluffy, so a scoop of it weighs far less than a scoop of sand. DE is a fine dust, so follow the handling directions on the bag.

Above-ground kit filters (Intex, Bestway) use their own cartridges or small sand tanks. See the Intex cartridge guide and the Bestway Flowclear filter guide.

Bigger filter, longer time between cleanings

A filter sized right at the minimum works, but it fills with dirt sooner, the pressure rises faster, and flow drops between cleanings. A larger filter spreads the same dirt over more area. That is why the calculator also shows the cartridge size for longer cycles. For cartridges, a practical choice is a filter between the residential minimum and the longer-cycle size.

There is no harm in a filter that is bigger than needed, as long as the plumbing fits. The cost is a higher purchase price and, for cartridges, larger replacement elements.

If the water stays cloudy even though the filter is the right size, the cause is usually chemistry or run time, not filter size. See cloudy pool water and the pump run time calculator.

Check the filter label against your pump

  • The flow rating on the filter label must be at least your pump's flow. A filter pushed past its rating filters poorly and can be damaged.
  • Check the maximum working pressure on the label. Hayward's S244T2, for example, lists 50 PSI.
  • Match the port size of the filter or valve to your pipes.
  • Write down the clean-filter pressure when you start. Most makers tell you to clean or backwash when the pressure rises a set amount above it. Your manual gives the number.

FAQ

What size pool filter do I need?

Divide your pump's flow by the filter's rate. At 50 gpm, that is at least 50 sq ft of cartridge, 25 sq ft of DE, or 2.5 sq ft of sand. Bigger is fine, and the filter's rated flow must be at least your pump's flow.

How much sand does a pool filter need?

The amount your filter's label or manual lists, because it depends on the tank. For example, Hayward lists 300 lb for its 24-inch S244T2 sand filter. Use the sand type the filter maker names.

How much DE do I put in my pool filter?

The amount on your DE filter's label or in its manual, added again after each backwash. Hayward lists 6 lb for its 48 sq ft ProGrid DE4820. Measure by weight, not by guess.

Can a pool filter be too big?

Not for filtering. A larger filter runs longer between cleanings. The only downsides are a higher price and, for cartridges, larger elements to replace. Make sure the ports and plumbing fit.

Sources

  • NSF, Proposed revision to NSF/ANSI/CAN 50, issue 219 (2025), quoting Table 6.4, maximum design filtration rates for cartridge filters: standards.nsf.org (PDF)
  • Hayward, ProSeries 24" sand filter S244T2 (3.14 sq ft, 62 gpm, 300 lb sand, 50 PSI): hayward.com
  • Hayward, ProGrid DE filter 48 sq ft DE4820 (96 gpm, 6 lb DE): hayward.com