What Size Cartridge Filter Do I Need? Sizing by Pool Gallons

What Size Cartridge Filter You Need

Size a cartridge filter by its filter area in square feet relative to your pool volume in gallons, not by the pump alone. A practical rule is about 1 square foot of filter area per 1500 to 2500 gallons of water. For most residential pools that points to a cartridge filter somewhere between 100 and 200 square feet. When you are between sizes, go bigger.

Bigger filter area is the single most useful lever you have. More square footage means lower pressure, longer stretches between cleanings, and a longer-lasting element.

Step 1: Know Your Pool Gallons

You cannot size a filter without the water volume. Use the right formula for your shape:

• Rectangular: length x width x average depth x 7.5
• Round: diameter x diameter x average depth x 5.9
• Oval: length x width x average depth x 6.7

Average depth is shallow end plus deep end divided by two. Write the number down. Everything below keys off it.

Step 2: Use the Sizing Table

This table maps pool gallons to a sensible cartridge filter area. It assumes a standard once or twice daily turnover. When two sizes fit, choose the larger one for longer runs between cleanings.

These ranges line up with common cartridge filter models. Pentair Clean & Clear ships in 75, 100, 150, and 200 square foot tanks. Hayward SwimClear comes in 100, 150, 225, and 325. Jandy CL and CV cover a similar spread. Pick the tank whose square footage lands in your recommended column. For a mid-size pool the Pentair Clean and Clear Plus 320 hits the sweet spot; smaller pools do well with the Hayward SwimClear C2030.

Step 3: Check the Flow Rating Against Your Pump

Filter area sets cleaning frequency and element life. The flow rating in GPM keeps the filter matched to the pump. The filter’s rated flow should equal or exceed the pump’s flow at your operating head. If the pump pushes more GPM than the filter is rated for, the element runs at high pressure and wears out fast.

If you do not know your pump’s flow, the safe move is to choose the larger filter. An oversized cartridge filter never causes a flow problem. An undersized one always does. For the general pump-to-filter sizing method across all filter types, see what size pool filter do i need.

Why Cartridges Reward Oversizing

Cartridge filters are not backwashed, so the only way to clear a loaded element is to pull it, rinse it, and periodically soak it. A larger square-foot rating spreads the same dirt load across more pleated media, so:

• Pressure rises more slowly, meaning fewer cleanings per season.
• Each element handles less stress, extending life toward the top of the 2 to 3 year range.
• Water clarity holds up under heavy bather load and oils.

There is no efficiency penalty for going bigger. The only costs are tank price and the physical footprint. For most owners that trade is worth it.

Don’t Forget the Element Brand

Once the tank is sized, the replaceable element inside still matters. Stick with Pleatco, Unicel, Filbur, or the OEM cartridge for your housing. Cheap generic elements often have thinner media that filters less and fails sooner, which undercuts the whole point of sizing carefully. When the time comes, our guide on when to replace pool filter cartridge covers the failure signs.

Quick Sizing Summary

1. Calculate pool gallons.
2. Find your row in the table and read the recommended square footage.
3. Confirm the filter’s GPM rating meets or beats your pump.
4. When between sizes, round up.

If you are still deciding between cartridge, sand, and DE before sizing, start with how to choose a pool filter.

Related Guides

• Pool Filter Size Calculator - work out the cartridge area your pool needs
• When to Replace Pool Filter Cartridge - element replacement signs
• What Size Pool Filter Do I Need - sizing across all filter types
• How to Choose a Pool Filter - cartridge vs sand vs DE