Pool Filter Size Calculator

Check pool filter inputs

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Pool preset:

Start with the closest pool and edit the sizing assumptions.

Sizing basis:

Choose whether to calculate circulation flow or size directly from a known pump flow.

Unit system:

Switch the input units without changing the underlying pool size or flow.

Pool volume:

Water volume used to compute turnover flow.

Turnover target:

Shorter turnover targets increase required circulation flow.

Known design flow:

Flow used directly for filter loading and common-size selection.

Primary filter type:

Select the media family you plan to buy or verify.

Bather and debris load:

Adjusts target flow, oversize headroom, and maintenance checks.

Pump/system flow to protect:

The calculator sizes against the larger of turnover demand and this protected pump flow.

Oversize margin:

Extra filter area above the minimum media loading requirement.

Smallest plumbing run:

Used only for the compatibility checks and JSON export.

Cleaning pressure rise trigger:

Reference trigger for maintenance guidance only.

psi

Display precision:

Adjust visible precision for estimates and exports.

Metric	Value	Use it for	Copy
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Filter type	Loading rate	Recommended area	Common size	Capacity margin	Fit	Copy
{{ row.filter }}	{{ row.loadingRate }}	{{ row.recommendedArea }}	{{ row.commonSize }}	{{ row.capacityMargin }}	{{ row.fit }}

Check	Status	Action	Reason	Copy
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A pool filter is sized by flow and media area, not by pool gallons alone. The water volume tells you how much flow is needed to circulate the pool within a target turnover time. The pump and plumbing then decide how much flow the equipment pad may actually deliver. The filter has to accept that design flow without forcing water through too little media.

Sand, cartridge, and diatomaceous earth filters use very different media areas. A sand tank may have only a few square feet of bed area because the media can run at a high flow per square foot. A cartridge filter often uses hundreds of square feet because pleated media is rated at a much lower flow per square foot. DE grids sit between those two in footprint and maintenance style.

Pool filtration diagram connecting pool volume, turnover flow, pump flow, and filter media area.

Turnover is a circulation planning concept: pool volume divided by time gives the flow needed for one pass through the system. It does not mean every water molecule is filtered once, and it does not replace water testing, skimming, brushing, or chemical balance. It does give a starting point for checking whether a filter can handle the flow required by the pool and by the pump.

Oversizing a filter usually helps residential service because it lowers media loading, slows pressure rise, and can extend cleaning intervals. Oversizing is not a license to ignore manufacturer maximum flow, backwash requirements, pipe limits, or local code. A filter that is too small can short-cycle, channel, clog quickly, or force the pump to operate outside a comfortable range.

Design flow: the GPM or L/min value the filter must safely handle.
Media loading rate: the allowed flow per square foot of filter area for the chosen media.
Area margin: extra filter area added above the minimum to reduce tight operation.
Clean pressure baseline: the reference pressure used later to decide when cleaning or backwashing is due.

How to Use This Tool:

Choose a profile or enter your pool volume, unit system, and turnover target.
Use turnover mode when you are sizing from pool gallons or liters, or known-flow mode when you already have a measured pump or filter flow.
Enter the protected pump flow so the selected filter is checked against the largest flow it may see in use.
Select sand, cartridge, or DE, then set bather/debris load, oversize margin, smallest pipe size, and pressure-rise cleaning trigger.
Read Sizing Ledger for the chosen media, Filter Options for all three media types, and Maintenance Checks for pump, pipe, turnover, margin, and cleaning guidance.

If the result says needs larger filter, tight, or review, do not round down. Compare the next catalog size, lower the pump flow where appropriate, or ask a pool professional to check the actual hydraulics.

Interpreting Results:

The Recommended Size is the nearest common size for the selected media after design flow and area margin are applied. Filter Options compares sand, cartridge, and DE on the same flow assumption, so the common size labels can look very different even when the flow is identical.

Pool filter result fields and interpretation
Output	Meaning	What to verify
Filter design flow	The flow used to size the filter after turnover, load, and pump protection.	Compare with a flow meter or the pump curve at real plumbing head.
Minimum media area	Design flow divided by the media loading rate.	Manufacturer ratings may be stricter than the generic model.
Recommended media area	Minimum area plus the selected margin and load allowance.	Choose the next catalog size at or above this area.
Capacity margin	How much rated flow remains above the design flow.	Negative or tight margin means the filter should be upsized or flow reduced.

A green sizing result is still an equipment planning estimate. Final selection should use the filter manual, pump curve, pipe layout, valve losses, heater or salt-system limits, and local requirements.

Technical Details:

Filter sizing begins with a flow requirement. In turnover mode, volume is divided by turnover hours and 60 minutes per hour. The selected bather or debris load can raise that flow. The design flow then protects against the pump flow entered by the user, because a filter must tolerate the flow the pump can send through it, not only the flow needed by the turnover target.

Media area follows from the loading rate. The calculator models high-rate sand at 15 GPM/ft2, cartridge at 0.35 GPM/ft2, and DE at 2 GPM/ft2. Those are planning rates, not a substitute for the filter label. Certified listings and manufacturer manuals may publish model-specific flow rates and effective areas that should control a purchase.

Formula Core:

The turnover path converts volume and target time to flow, then converts flow to filter area.

turnoverFlow = \frac{poolVolume}{turnoverHours * 60}

recommendedArea = \frac{designFlow}{loadingRate} * (1 + margin)

For a 24,000 gallon pool with an 8 hour target, turnover flow is 24,000 / 8 / 60 = 50 GPM before load adjustment. If the protected pump flow is 60 GPM, the design flow becomes 60 GPM. At a cartridge planning rate of 0.35 GPM/ft2 with 25% margin, recommended area is about 214 ft2, so a 200 ft2 cartridge is tight and a larger common size is safer.

Pool filter media rates and sizing cautions
Media	Planning rate	Sizing caution
High-rate sand	15 GPM/ft2	Needs proper tank diameter, sand grade, and backwash flow.
Cartridge	0.35 GPM/ft2	Large area supports lower pressure rise and longer cleaning intervals.
DE	2 GPM/ft2	Requires correct DE handling, grid care, and backwash or cleaning procedure.

The Maintenance Checks tab adds practical screens for pump-filter compatibility, pipe reference limits, turnover target, area margin, cleaning interval, and media fit. These checks do not replace a hydraulic design, but they catch common contradictions such as a filter that clears turnover math while still being undersized for pump output.

Limitations and Accuracy Notes:

This is a planning calculator for filter area and common residential size comparison. Final equipment selection should use the specific filter rating, pump curve, total dynamic head, plumbing size, heater limits, sanitizer flow limits, pressure rating, local code, and advice from a qualified pool professional when the system is public, commercial, unusually large, or hydraulically complex.

Worked Examples:

Family inground pool: A 24,000 gallon pool with an 8 hour turnover target and 60 GPM protected pump flow may point to a cartridge size above the bare minimum. Filter Options shows whether sand or DE would need a different catalog size for the same flow.

Known-flow equipment pad: If a flow meter or pump curve supports 65 GPM, known-flow mode skips volume-based turnover math and sizes media from that flow. Maintenance Checks still help you confirm whether turnover and pipe assumptions make sense.

Troubleshooting tight margin: When capacity margin is near zero, select a larger filter, reduce pump RPM if the equipment allows it, or revisit the turnover target. Do not rely on clean-filter pressure alone because dirty media raises resistance over time.

FAQ:

Should I size the filter from pool volume or pump flow?

Use both when possible. Pool volume sets the turnover flow, while pump flow protects against the actual flow the filter may receive.

Why does a cartridge filter need so many square feet?

Cartridge media is rated at a much lower flow per square foot than sand in this planning model, so it needs more surface area for the same GPM.

When should I clean or backwash the filter?

Use the pressure rise above the clean baseline from your filter manual or service practice. The cleaning interval shown here is only a rough planning screen.

Glossary:

Turnover flow: The flow needed to circulate the pool volume within a selected number of hours.
Design flow: The flow used for sizing after turnover, load, and pump protection are considered.
Loading rate: The allowed flow per square foot of filter media area.
Capacity margin: The filter's rated flow capacity minus the design flow.