What Size Pool Filter Do I Need? - Sizing Guide by Pool Gallons
Pool filter size is determined by your pool's volume and pump flow rate - not pool dimensions. This guide gives you the formula, a sizing table by gallons, and the minimum filter area for every common pool size.
The Sizing Rule: Bigger Is Always Better
Unlike pool pumps (where oversizing wastes electricity), pool filters benefit from being larger than the minimum required. A filter that is twice the size your pool requires will:
- Run at lower pressure
- Need backwashing or cleaning less often
- Last longer between filter media replacements
- Filter finer particles more effectively
There is no meaningful downside to an oversized filter beyond the higher purchase price.
Sand Filter Sizing by Pool Volume
Sand filters are sized by tank diameter. Larger diameter = larger filter area = more filtration capacity.
| Pool Volume | Minimum Tank Size | Recommended Tank Size |
|---|---|---|
| Up to 10,000 gallons | 19 inch | 21 inch |
| 10,000-15,000 gallons | 21 inch | 24 inch |
| 15,000-25,000 gallons | 24 inch | 24-27 inch |
| 25,000-35,000 gallons | 27 inch | 27-30 inch |
| 35,000+ gallons | 30 inch | 30-36 inch |
Common residential models by size:
| Tank Size | Hayward | Pentair |
|---|---|---|
| 19 inch | ProSeries S180T | Triton II TR-40 |
| 21 inch | ProSeries S210T | Triton II TR-60 |
| 24 inch | ProSeries S244T | Triton II TR-100 |
| 27 inch | ProSeries S270T | Triton II TR-140 |
Cartridge Filter Sizing by Pool Volume
Cartridge filters are sized by total filter area in square feet. More square footage = larger filtering surface.
| Pool Volume | Minimum Filter Area | Recommended Filter Area |
|---|---|---|
| Up to 10,000 gallons | 100 sq ft | 150 sq ft |
| 10,000-20,000 gallons | 200 sq ft | 300 sq ft |
| 20,000-30,000 gallons | 300 sq ft | 400 sq ft |
| 30,000+ gallons | 400 sq ft | 500+ sq ft |
Common cartridge filter models:
| Filter Area | Hayward | Pentair |
|---|---|---|
| 100 sq ft | Star-Clear C1200 | Clean & Clear 100 |
| 200 sq ft | Star-Clear C2002 | Clean & Clear Plus CC200 |
| 320 sq ft | Star-Clear C3002 | Clean & Clear Plus CC320 |
How to Calculate Your Pool Volume
You need the pool volume in gallons to use these tables. If you do not know your pool’s exact volume:
Rectangular pool: Length (ft) x Width (ft) x Average Depth (ft) x 7.48
Circular pool: Diameter (ft) x Diameter (ft) x Average Depth (ft) x 5.9
Oval pool: Length (ft) x Width (ft) x Average Depth (ft) x 6.7
Example: A 20 ft x 40 ft rectangular pool with 5 ft average depth = 20 x 40 x 5 x 7.48 = 29,920 gallons (approximately 30,000 gallons).
Above-Ground Pool Filter Sizing
Above-ground pools are typically 10,000-20,000 gallons. The most common filter setups:
| Pool Size | Recommended Filter |
|---|---|
| Small (up to 5,000 gal) | 10-16 inch sand filter |
| Medium (5,000-12,000 gal) | 19-21 inch sand filter or 100-150 sq ft cartridge |
| Large (12,000-20,000 gal) | 21-24 inch sand filter or 150-200 sq ft cartridge |
Intex sand filters (10-12 inch) are sized for Intex-brand above-ground pools. They are too small for permanent above-ground pools in the 12,000+ gallon range.
Matching Filter Size to Pump Size
The filter must be able to handle the full flow rate of your pump without excessive pressure. Check the filter’s maximum flow rate rating (on the label) against your pump’s output.
A filter rated to 80 GPM paired with a 100 GPM pump will run at permanently high pressure. The pump will eventually overwhelm the filter and force debris through the media. Size the filter to handle your pump’s maximum flow rate at the low end of its normal operating pressure (below 15 PSI clean baseline is ideal).
Related Guides
- How Long Should a Pool Filter Run? - filter run time by pool size
- Pool Filter Pressure Too High - when an undersized filter causes pressure problems
- How to Change Pool Filter Sand - if replacing sand in an existing filter
- Pool Filter Maintenance Guide - full maintenance schedule
Frequently Asked Questions
What size pool filter do I need?
What size sand filter for a 20,000 gallon pool?
What size cartridge filter for my pool?
Can my filter be too big for my pool?
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