What Size Sand Filter Do I Need? Sizing Chart by Pool Volume

Sand filters are sold by tank diameter, and picking the wrong diameter is the single most common mistake pool owners make when replacing a filter. This guide is the sand filter version of our broader what size pool filter do I need guide, which covers sizing across all three filter types. If you have already decided on sand, everything below is specific to sand filter tanks, flow rates, and the models actually on the market.

The Sizing Rule in One Paragraph

Two numbers decide your sand filter size. First, your pump’s flow rate: the filter’s maximum design flow must match or exceed what the pump pushes, otherwise water rams through the sand bed too fast to be cleaned. Second, your pool volume: the whole system should turn over the entire pool in 8 to 10 hours. Work out both, then buy the tank that satisfies the larger requirement. When your pool lands between two sizes, take the bigger tank. Nobody has ever regretted a slightly oversized sand filter.

Sand filters clean effectively at about 15 to 20 gallons per minute per square foot of filter surface. A bigger tank means more surface area, which means the same pump moves water through the bed more slowly and traps finer debris. That is the entire physics of the decision.

Sand Filter Size Chart by Pool Volume

Find your pool volume in gallons or litres, then read across. If you do not know your volume, multiply length x width x average depth in feet, then multiply by 7.5 for gallons.

A quick sanity check with turnover: a 20,000 gallon pool needs 20,000 / 480 minutes = about 42 GPM to turn over in 8 hours. A 21 inch tank rated around 50 GPM handles that with margin. If your pump only achieves that flow when running flat out, or you plan to run shorter daily cycles, step up one size. Our guide on how long to run your pool filter shows how turnover time translates into daily runtime and electricity cost.

The chart answers the metric question we see constantly: a 50,000 litre pool is roughly 13,200 gallons. That technically fits the 19 to 21 inch band, but it sits close enough to the boundary that a 24 inch tank is the smarter buy. You get lower operating pressure, backwash sessions spaced further apart, and room for a pump upgrade later.

Above-Ground vs Inground: The Sizing Difference

The turnover math is identical, but the market splits the hardware.

Above-ground pools are smaller (typically 3,000 to 15,000 gallons), run smaller 1 to 1.5 HP pumps, and usually pair with 16 to 19 inch tanks sold as pump-and-filter combo systems with hose fittings rather than hard plumbing. A 3,400 gallon above-ground pool, another question we get often, needs only about 7 GPM for an 8 hour turnover, so a 16 inch tank is comfortably oversized already. The Hayward S180T above-ground sand filter is the standard pick for larger above-ground pools up to about 15,000 gallons. For a wider look at above-ground options across filter types, see our best above-ground pool filter roundup.

Inground pools are bigger, run higher-flow pumps through longer plumbing runs, and use 21 to 30 inch tanks with 1.5 or 2 inch plumbing connections. The pump matters more here: an inground 1.5 HP pump can push 70+ GPM at low head, which would overwhelm a small tank. Always size the inground filter against the pump curve, not just the pool volume.

One trap to avoid: above-ground filter systems are cheaper, and some inground owners try to save money with one. Do not. The tanks are not rated for the pressure an inground pump develops, and the hose fittings will not hold.

Sand Filter Sizes by Brand and Model

The two brands that dominate residential sand filtration are Hayward and Pentair. We compare them head to head in our Hayward vs Pentair sand filter guide, but here is how their model numbers map to tank sizes and pool fit.

The Hayward S244T is our top pick for a reason: the 24 inch tank covers the bulk of residential inground pools with margin to spare. On the Pentair side, the Pentair Triton II TR-100 is the go-to for large pools above 30,000 gallons where a 24 inch tank starts running out of headroom.

Why Slightly Oversized Beats Undersized Every Time

Undersizing is the common and expensive mistake, and it usually happens because a smaller tank saves $50 to $100 at checkout. Here is what that saving costs you:

• High pressure, constantly. An undersized filter runs near the top of its pressure range, which strains the tank, the multiport valve, and the pump.
• Poor filtration. Water forced through the sand bed too quickly channels past the media, so fine debris returns to the pool and the water never quite sparkles.
• Endless backwashing. A small bed loads fast, so pressure climbs quickly and you backwash every week or two instead of every 4 to 6 weeks, wasting hundreds of gallons each time.
• Shorter sand life. A hard-driven bed compacts and channels sooner, so you replace the sand more often.

An oversized filter has exactly one downside, the upfront price. It runs at lower pressure, filters more finely, and stretches both backwash intervals and sand life. Sizing up one tank diameter is the best value upgrade in the whole decision.

Tank Size and Sand Quantity

Tank diameter also fixes how much media you buy on day one and at every sand change. The 16 inch tank takes a single 50 lb bag, the 19 inch takes two, the 21 inch takes three, and the 24 inch S244T takes four bags (200 lbs). The big 27 and 30 inch tanks take 300 and 350 lbs. Every tank is filled only about two thirds full, leaving a freeboard space above the bed for water to distribute during filtration. The exact figure is on a label on the tank itself, and our how much sand for a pool filter chart lists quantities for every major model, plus reduced quantities if you use ZeoSand or glass media.

Factor the media into your budget: sand for a 24 inch tank costs about $48 to $60, and you will replace it every 3 to 5 years.

The Buying Checklist

1. Calculate pool volume in gallons (or convert litres by dividing by 3.785).
2. Divide volume by 480 to get the GPM needed for an 8 hour turnover.
3. Check your pump’s flow rate and take the larger of the two numbers.
4. Pick the tank whose design flow meets that number, then go one size up if you are near a boundary.
5. Confirm the valve and plumbing connections match your pipe size (1.5 or 2 inch).

That is the entire sizing decision. For everything that happens after the tank arrives, from first fill to first backwash, start with our full sand filter hub.

Related Guides

• Pool Filter Size Calculator - tank size, sand load, and bag count from your pool volume
• Sand filters: complete guide
• How much sand for a pool filter
• What size pool filter do I need (all filter types)
• How long to run your pool filter
• Hayward vs Pentair sand filters
• Best above-ground pool filters