How many gallons your pool actually holds — sloped floors included, plus the supplies to keep it clear.
Pool volume in gallons = surface area × average depth × 7.48. Average depth on a pool that slopes is the shallow-end water depth plus the deep-end water depth, divided by two. A 16 × 32 ft rectangular pool running 3 ft to 8 ft holds about 21,100 gallons; a 24 ft round above-ground pool filled to 4 ft holds about 13,500 gallons. The calculator below does it for rectangle, round, oval, and kidney shapes, and sizes a maintenance list to match.
Measure the water, not the wall. An above-ground pool with a 52-inch wall usually holds about 46–48 inches of water — that is 3.8 to 4 ft, not 4.3 ft.
21,064 gallons ÷ 480 minutes = 44gallons per minute to circulate the whole pool once in 8 hours, the usual residential target. Your filter's rated flow should meet or exceed that, and pipe diameter caps what the system can really move — a pump rated above what the plumbing passes just burns electricity.
Averaging the shallow and deep readings is exact when the floor drops at a steady grade. If your pool has a flat shallow shelf that breaks into a sharp hopper, this figure runs high — the shelf covers more floor area than the hopper does. Measure a third depth at the midpoint and average all three, or run the shallow half and the deep half through the calculator separately and add the results.
15,000 – 25,000 gallons · Standard residential inground
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Start here — every chemical below is dosed off a test reading, not off gallons alone
Tip: Test strips are fine for weekly checks. A drop-based kit reads chlorine and pH more precisely when something is off.
About 3–5 tabs per week at 15,000 – 25,000 gallons
Tip: Tabs go in a floater or an inline feeder — never straight into the skimmer, where they sit against the pump seals and corrode them.
Holds the tabs and meters them out slowly instead of dumping all at once
Roughly 2–3 bags per shock treatment at this volume — buy a multi-pack to cover the season
Tip: Shock after dark. Sunlight burns off unstabilized chlorine before it finishes working.
One bottle covers a typical season at this volume
Brushing the walls and floor is what keeps algaecide and chlorine from having to do all the work
Read before you dose
•Quantities above are what to buy for a pool this size — they are not doses. Chemical concentration varies by product and brand.
•Dose to the product label and to what your test kit reads. Water temperature, sunlight, rainfall, and how many people swim all move the number.
•Balance pH and total alkalinity before chlorinating. Chlorine loses much of its effect above roughly pH 7.8.
•Never mix chemicals in the same container, and add chemicals to water — never water to chemicals.
• Surface area: 32 × 16 = 512 sq ft
• Average depth: (3 + 8) ÷ 2 = 5.5 ft
• Volume: 512 sq ft × 5.5 ft = 2,816 cubic feet
• Gallons: 2,816 cubic feet × 7.48 gallons per cubic foot = 21,064 gallons
• Liters: 21,064 × 3.785 = 79,735 liters
• Turnover flow: 21,064 ÷ (8 hours × 60 minutes) = 44 GPM
This is where most pool volume estimates go wrong. People measure the deep end, plug that in, and end up with a number 30 to 40 percent too high — then over-buy chemicals all season on the strength of it.
A pool that slopes has one depth that matters for volume: the average. Measure the water depth at the shallow end, measure it again at the deepest point, add them, divide by two. Averaging that way is exact when the floor drops at a constant grade from one end to the other, which covers most vinyl-liner pools and most simple slope designs.
It stops being exact on a hopper-bottom pool — the shape with a long flat shallow shelf, a steep transition, then a flat deep bottom under the diving end. There the shallow shelf covers far more floor area than the deep hopper does, so a straight two-point average weights the deep end more than the pool actually does and the total comes out high. Two ways to handle it:
One more thing worth checking: measure to the water line, not to the coping or the top of the wall. Pools run several inches below their structural height, and that gap comes straight off your volume.
A 24 ft round pool sold as a “24 × 52” has a 52-inch wall. It does not hold 52 inches of water. Manufacturers direct you to fill to roughly the middle of the skimmer opening, which leaves about 4 to 6 inches of dry wall above the surface — so actual water depth lands closer to 46 to 48 inches.
Volume scales directly with depth, so losing 4 inches off a 52-inch wall takes roughly 8 percent of the water with it, and losing 6 inches takes about 12 percent. On a 24 ft round that is the difference between about 14,700 gallons at full wall height and about 13,500 gallons at a realistic 4 ft fill. Order chemicals against the box number and you are dosing a pool that does not exist.
The stated diameter is worth a second look too. It is often measured across the outside of the top rail, while the water sits inside the wall — a few inches narrower. It is a smaller error than the depth one, but it runs in the same direction. Measure your own water and use that.
Turnover rate is the time it takes the pump to push a volume of water equal to the whole pool through the filter. Eight hours is the standard residential target; public pools are typically held to shorter turnovers under health codes.
The math is one division. Take the pool volume in gallons and divide by the turnover time in minutes. For an 8-hour turnover that is 480 minutes, so a 20,000-gallon pool needs about 42 gallons per minute and a 13,500-gallon above-ground needs about 28 GPM.
Two things to know before you shop on that number. The filter has its own rated flow, and it should meet or exceed the pump's — a pump that outruns its filter pushes water through too fast to clean it properly. And plumbing diameter puts a hard ceiling on flow no matter what the pump is rated for, so an oversized pump on undersized pipe mostly converts electricity into noise. Sizing to the turnover figure, rather than above it, is usually the right call.
Every figure below is this page's formula applied to the stated dimensions, rounded to the nearest hundred gallons. Use them as a sanity check on your own measurement, not as a substitute for it.
Multiply the pool's surface area by its average depth to get cubic feet, then multiply by 7.48 to get US gallons. For a rectangle that is length × width × average depth × 7.48. On a pool that slopes, average depth is the shallow-end water depth plus the deep-end water depth, divided by two. A 16 × 32 ft rectangular pool sloping from 3 ft to 8 ft holds roughly 21,100 gallons.
Measure the water depth — not the wall height — at the shallow end and again at the deepest point, then average the two. That average is exact when the floor slopes at a constant grade from one end to the other. If your pool has a flat shallow shelf that drops sharply into a hopper, the simple average runs high, because the shallow shelf covers more floor area than the deep hopper does. In that case take a third measurement at the midpoint and average all three, or treat the shallow half and the deep half as separate rectangles and add their volumes.
The capacity printed on the box is generally calculated at the pool's full wall height, and an above-ground pool is never filled that high. Manufacturers direct you to fill to about the middle of the skimmer opening, which leaves roughly 4 to 6 inches of dry wall. On a 52-inch wall that puts actual water depth closer to 46–48 inches. Volume scales directly with depth, so the real number lands about 10 percent under the wall-height figure. Measure your actual water depth and use that.
About 5,300 gallons at 4 feet of water depth: π × 7.5² × 4 × 7.48. The same pool at 42 inches of water holds about 4,600 gallons. Round pools gain and lose volume quickly with depth, so measure the water rather than assuming the wall height.
Turnover rate is how long the pump takes to circulate a volume of water equal to the entire pool. Eight hours is the usual residential target. Divide the pool's gallons by 480 (8 hours × 60 minutes) to get the minimum flow rate in gallons per minute. A 20,000-gallon pool needs roughly 42 GPM for an 8-hour turnover. The filter's rated flow should meet or exceed the pump's output, and plumbing diameter caps what the system can actually move.
That depends on the concentration of the specific product, plus water temperature, sunlight and how heavily the pool is used, so there is no single correct figure by volume alone. Manufacturers of 3-inch stabilized tablets generally direct one tablet per 5,000 gallons per week as a starting point, adjusted by what your test kit reads. This calculator sizes the shopping list for a pool your size — always dose to the product label and your test results, not to a number from a website.
Written and maintained by the BuildGuiders team. Volumes come from standard pool-industry geometry (7.48 gallons per cubic foot; 0.893 and 0.45 shape factors for oval and kidney pools). Product recommendations are researched and compared against manufacturer specifications and verified buyer feedback — we do not lab-test pool chemicals, and nothing here is a dosing instruction. Follow the label on the product you buy and your own test readings.