Pool Filter Size Calculator
Determine the right filter size for your pool. Compare sand, cartridge, and DE filter types side by side.
Filter Size Comparison
| Filter Type | Min. Size (sq ft) | Filtration | Cost | Maintenance | Lifespan |
|---|---|---|---|---|---|
| Sand Filter | 25 sq ft | 20-40 microns | Lowest | Backwash weekly | 5-7 years (media) |
| Cartridge Filter | 15 sq ft | 10-15 microns | Moderate | Clean 2-4x/year | 2-3 years (cartridge) |
| DE Filter | 10 sq ft | 2-5 microns | Highest | Backwash + add DE powder | 7-10 years (grids) |
Filter Type Details
- +Cheapest upfront cost
- +Low maintenance
- +Easy to operate
- -Lowest filtration quality
- -Requires backwashing (water waste)
- -Sand needs replacement every 5-7 years
- +No backwashing needed
- +Good filtration (10-15 microns)
- +Energy efficient (lower pressure)
- -Cartridges need periodic replacement
- -Must be cleaned by hand
- -Higher replacement cost than sand
- +Best filtration quality (2-5 microns)
- +Crystal-clear water
- +Longest grid lifespan
- -Most expensive upfront
- -Requires DE powder after backwashing
- -More complex maintenance
How It Works
This calculator determines the minimum filter area (in square feet) needed for your pool based on the required flow rate. First, it calculates the GPM your pump needs to turn over the pool in your desired time, then sizes each filter type accordingly.
Required GPM = Pool Volume / Turnover Hours / 60. For a 20,000-gallon pool with an 8-hour turnover, that is about 42 GPM.
Each filter type handles flow differently. Sand filters need the most area (0.5 sq ft per GPM), cartridge filters are in the middle (0.3 sq ft per GPM), and DE filters need the least (0.2 sq ft per GPM) because they filter at the finest level.
We recommend sizing up by at least 25-50% for better performance, longer cleaning intervals, and lower operating pressure.
Frequently Asked Questions
What size pool filter do I need?
Filter size is determined by the required flow rate (GPM) of your pool pump. The filter must handle the pump's GPM without excessive pressure. Sand filters need about 0.5 sq ft per GPM, cartridge filters need 0.3 sq ft per GPM, and DE filters need 0.2 sq ft per GPM. Always size up if you're between sizes.
Which pool filter type is best?
It depends on your priorities. Sand filters are the cheapest and easiest to maintain but provide the least filtration. Cartridge filters offer a good balance of filtration quality and convenience with no backwashing. DE filters provide the best water clarity (filtering particles as small as 2 microns) but cost more and require DE powder.
How often should I clean my pool filter?
Sand filters should be backwashed when the pressure gauge reads 8-10 psi above the clean starting pressure, typically weekly during heavy use. Cartridge filters should be removed and hosed off every 2-4 months. DE filters need backwashing similar to sand and require fresh DE powder added after each backwash.
Can I oversize my pool filter?
Yes, and it's actually recommended. An oversized filter provides better filtration, lower operating pressure, longer cleaning intervals, and extended filter media life. There is no practical downside to a larger filter — the only consideration is physical space and upfront cost. A filter that's 50% larger than the minimum is a good target.