# Pool Filter Size Calculator

Pool filter size calculator for sand, cartridge, and DE filters. Enter pool gallons and turnover time to get the right filter size, flow rate, and pump HP.

## What this calculates

Size your pool filter correctly and cut cleaning time in half. This pool filter size calculator works out the required flow rate (GPM) from your pool volume and turnover time, then recommends the right filter size for sand, cartridge, or D.E. filters. Oversize a little if you can, because a larger filter traps more dirt between cleanings and runs at lower head pressure, which saves energy.

## Inputs

- **Pool Volume** (gallons) — min 500, max 200000 — Use the pool size calculator if you don't know your volume
- **Desired Turnover Time** — options: 6 hours (commercial / heavy use), 8 hours (residential standard), 10 hours (light use / variable speed pump), 12 hours (minimum circulation) — Industry standard is 8 hours for residential pools
- **Filter Type** — options: Sand filter, Cartridge filter, D.E. (Diatomaceous Earth)

## Outputs

- **Required Flow Rate** — Minimum gallons per minute for this turnover time
- **Recommended Filter Size** — formatted as text — Square feet (cartridge/DE) or tank diameter (sand)
- **Minimum Pump Size** — formatted as text — Pump horsepower needed to reach the required GPM
- **Filter Max Flow Rating** — Upper flow the recommended filter can handle
- **Maintenance Note** — formatted as text

## Details

Pool Filter Sizing Rules

Every filter type has a maximum flow rate per square foot (or per square foot of tank surface). Go above those limits and water blasts through too fast to filter properly, letting dirt and algae through:

  - Cartridge filter: 0.375 GPM per sq ft for quality filtration (3/8 GPM/sq ft rule)

  - Sand filter: 15-20 GPM per sq ft of tank surface area (use 15 for best clarity)

  - D.E. filter: 2 GPM per sq ft of filter grid area

Required Flow Rate

Required GPM = Pool Gallons / (Turnover Hours x 60). The industry standard turnover is 8 hours for residential pools, 6 hours for commercial. A 20,000 gallon pool needs 41.7 GPM for an 8-hour turnover, or 55.6 GPM for a 6-hour turnover.

Pool Sand Filter Size Chart

Sand filter tanks are sized by tank diameter in inches. Each tank has a max flow rate rating:

| Tank Diameter | Sand Needed | Max Flow (GPM) | Good For |
|---|---|---|---|
| 16 in | 100 lbs | 30 GPM | Up to 14,000 gal |
| 19 in | 150 lbs | 40 GPM | Up to 19,000 gal |
| 22 in | 200 lbs | 50 GPM | Up to 24,000 gal |
| 24 in | 250 lbs | 60 GPM | Up to 29,000 gal |
| 26 in | 300 lbs | 70 GPM | Up to 34,000 gal |
| 30 in | 450 lbs | 90 GPM | Up to 43,000 gal |
| 36 in | 650 lbs | 130 GPM | Up to 62,000 gal |

Hayward Pool Sand Filter Size Chart

Hayward is the most common pool filter brand in North America. The hayward pool sand filter size chart maps to the generic sizing above:

  - Hayward S166T (16 in): 35 GPM max

  - Hayward S180T (18 in): 42 GPM

  - Hayward S210T (21 in): 55 GPM

  - Hayward S220T (22 in): 55 GPM

  - Hayward S244T (24 in): 65 GPM

  - Hayward S270T (27 in): 80 GPM

  - Hayward S310T (31 in): 112 GPM

Hayward and Pentair Cartridge Filter Sizing

Hayward SwimClear, Pentair Clean and Clear, and Sta-Rite System 3 all follow the same 0.375 GPM/sq ft rule. The hayward pool filter size chart and pentair pool filter size chart for cartridges look like:

  - 100 sq ft cartridge: ~38 GPM max

  - 150 sq ft cartridge: ~56 GPM

  - 200 sq ft cartridge: ~75 GPM

  - 300 sq ft cartridge: ~113 GPM

  - 400-425 sq ft cartridge: ~150 GPM

  - 520 sq ft cartridge: ~195 GPM

## Frequently Asked Questions

**Q: What size pool filter do I need for a 15,000 gallon pool?**

A: For a 15,000 gallon pool with an 8-hour turnover, you need 31.3 GPM. That points to a 100-120 sq ft cartridge filter, a 19-22 inch sand filter, or a 48 sq ft D.E. filter. Always pick a filter rated for slightly more flow than required so it doesn't run at its max capacity constantly.

**Q: What size pool filter do I need for a 24,000 gallon pool?**

A: A 24,000 gallon pool at 8-hour turnover needs 50 GPM. That means a 150 sq ft cartridge (like a Hayward C150S), a 24-26 inch sand tank (Hayward S244T or S270T), or a 48-60 sq ft D.E. filter. Step up to a 22-inch sand filter or 150+ sq ft cartridge if you have a lot of trees, pets, or heavy bather load.

**Q: What size pool filter do I need for a 30,000 gallon pool?**

A: A 30,000 gallon pool at 8-hour turnover needs 62.5 GPM. The sweet spot is a 200 sq ft cartridge (Hayward SwimClear C200S, Pentair Clean and Clear 200), a 27-30 inch sand filter (Hayward S270T or S310T), or a 60 sq ft D.E. Grid filter. At this size, a variable-speed pump saves hundreds per year vs single-speed.

**Q: How do I read the Hayward pool sand filter size chart?**

A: Hayward sand filters use S-series model numbers where the digits indicate tank diameter in inches. S166T is a 16-inch tank (~35 GPM max), S244T is 24 inches (65 GPM), S310T is 31 inches (112 GPM). Pick a model whose max flow exceeds your required GPM but doesn't blow past your pump's actual output. Pentair's Tagelus and Sand Dollar series use similar logic.

**Q: Is it OK to oversize a pool filter?**

A: Yes, and it's usually a good idea. An oversized pool filter traps more dirt between cleanings, runs at lower head pressure (which saves pump energy), and filters finer particles because water moves through it more slowly. The downside is upfront cost: a 420 sq ft cartridge filter for a 15,000 gal pool costs 2x a 100 sq ft filter but lasts longer between cleanings.

**Q: Cartridge, sand, or D.E. filter: which is best?**

A: D.E. filters clean finest (down to 2-5 microns), cartridges are mid-range (10-15 microns), sand is coarsest (20-40 microns with a clarifier). Cartridges are easiest to maintain (hose off, no backwash). Sand is cheapest to run but needs weekly backwashing. D.E. is best water quality but needs monthly backwash and fresh D.E. powder each time.

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Source: https://vastcalc.com/calculators/everyday/pool-filter
Category: Everyday Life
Last updated: 2026-04-08