Pool Filter Size Calculator
Last updated 15 October 2026
Enter circuit flow and an exact filter rating to check the flow limit.
Your result will appear here
Enter your measurements, then choose Calculate.
Compare your circuit flow with the filter’s documented limit.
Still unknown or unconfirmed
Formula, sources and blank printable worksheet
FILTER-1: compare actual Q with exact model rating. Equivalent capacity = rated GPM × 60 × scenario hours. Area screen = Q / documented rate.
Calculation version 1.0 uses historical engineering references for arithmetic, not current residential law.
- Clean & Clear Plus guide, printed p. 12: CCP240 90 GPM and model-specific pressure loss https://flowandfiltrationsolutions.pentair.com/content/dam/extranet/nam/pentair-pool/residential/filters/clean-and-clear-family/clean-and-clear-plus/clean-and-clear-plus-guides-manuals/clean-and-clear-plus-install-guide-english.pdf
- Sta-Rite Engineering and Design Manual, second edition, 2003, printed pp. 2, 27, 29, 36-40, 44 https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/manuals/training/Sta-Rite%20Engineering%20and%20Design%20Manual.pdf
| Quantity / unit | Reading | Source and date |
|---|---|---|
| Circuit flow, US GPM | ________________ | ________________ |
| What this flow represents | ________________ | ________________ |
| Exact filter model | ________________ | ________________ |
| Model-rated flow, US GPM | ________________ | ________________ |
| Exact manual reference | ________________ | ________________ |
Mark missing measurements Unknown. Keep exact model, source revision and assumptions with this worksheet. Report a calculation or source correction with reproducible inputs.
This pool filter size calculator compares flow with a documented model rating. It does not select a filter from pool gallons alone. It also does not identify a replacement cartridge by its length and diameter.
Enter actual or required flow and label which it is. Add the exact filter model, its rated flow and manual. A known flow below that rating passes that one comparison. Other equipment limits and pressure loss may still be unknown. Filter area, maximum pressure and flow capacity are different measures; none can silently replace another.
On this page6
Pool filter size calculator inputs
Start with the pool pump size calculator for a required circulation target. Use the flow-rate guide if you need actual operating flow. A pump can deliver more than the target, so check the filter against actual flow once it is known.
Choose sand, cartridge or DE to identify the type. Then enter data for the exact model. There is no one flow-per-area factor for all filters of a type. This tool uses an area rate only when its source fits the model and duty. Keep those conditions with the rate.
Filter size calculator worked reference
The Clean & Clear Plus manual, printed page 12 lists the CCP240 at 90 GPM with 240 square feet of filter area. The current Pentair table agrees for item 160310.
At an illustrative 8-hour period, 90 × 60 × 8 = 43,200 US gallons of equivalent circulated volume. A flow of 31.25 GPM is below the known filter rating. It does not establish compatibility for unknown heaters, cleaners, suction fittings or the rest of the circuit.
| Check | Meaning |
|---|---|
| Actual GPM versus rated GPM | A model-specific flow comparison |
| Filter area in ft² | Area of filtering material, not pool surface |
| Operating pressure rating | Pressure boundary, not a flow setting |
| Pressure drop at actual flow | Resistance added to the circulation path |
Area and dirt capacity
Area can affect the filtering surface and time between service. It cannot override the maker's model table. The Pentair page has a general area-rate footnote. It also has exact ratings.
The CCP240 table controls this example. Multiplying area by an unrelated factor would give a different limit with no support for this model.
If a specific manual supplies a usable filtration rate, the screening equation is flow ÷ rate = required area. Record its units and conditions. Treat this as a screen, not permission to exceed the selected model's flow rating.
Pressure loss and cleaning
Use the filter's pressure-drop curve at the same flow being checked. Do not add a guessed filter allowance to the circuit. A dirty filter can alter resistance, but the change must come from a stated measurement or source.
Keep the manual's cleaning and space requirements with the model. Do not loosen a clamp or remove a lid under pressure. Read how to shut down and release pressure before opening it. The cited manual gives that sequence for its own family. This sizing tool is not a service procedure.
FAQ
Does a large filter force a high flow?
A filter rating is not a commanded flow. Actual flow comes from the pump and circuit operating together. A filter with a higher documented capacity does not prove that the existing pump will reach it. Measure flow or use the matching pump and system curves.
Can I use pressure to calculate GPM?
One pressure reading is not enough. A filter-loss curve needs the pressure drop across that filter. A pump curve needs pump head and speed. A lone filter gauge gives neither complete input. Keep the reading method and its limits beside the result. A pressure number alone is not GPM.
Verdict on filter size
The pool filter size calculator checks documented flow limits without turning area into a universal rating. Save the exact model and source. If volume is missing, start with water measurements. Unknown equipment data remains visible on the printed record. Calculation version 1.0.