Pool Volume Calculator

Pool volume calculator for rectangle, round, oval and kidney pools: enter the dimensions in feet or meters and get the volume in US gallons and litres, plus surface area and average depth.

Quick answer

Pool volume = surface area × average depth, in the same units, then converted. A 32 × 16 ft rectangular pool that slopes from 3 ft to 6 ft averages 4.5 ft deep and holds 17,235 US gallons (65,242 litres). A 24 ft round pool with 4 ft of water holds 13,536 gallons. Enter your own shape and measurements above for the exact figure in both units.

Your Pool

Shape

Measure in

Length (ft)

Width (ft)

Water depth (ft)

Shallow end

Deep end

Flat-bottomed above-ground pool? Put the same number in both boxes. Measure the water you actually keep in it, not the height of the wall — most above-ground pools run 6 inches (15 cm) below the top rail.

Your Pool Holds

17,235

US gallons

65,242

litres

512 sq ft

surface area

4.5 ft

average depth

Measure your pool above and the volume is saved in your browser, so the pool chemical calculator, salt calculator and cyanuric acid calculator open with it already filled in. A volume you typed into one of those pages yourself stays as you left it. Readings and settings you picked there are remembered too, and none of them block a fresh measurement. Either way it stays on this device — nothing about your pool is sent anywhere.

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The Number Every Other Pool Number Depends On

Almost nothing you do to a pool can be worked out without knowing how much water is in it. Chlorine, acid, alkalinity increaser, stabilizer and salt are all dosed in parts per million, and a part per million is a milligram per litre — so every dose is your volume multiplied by how far the reading has to move. Get the volume 20% wrong and every dose you ever calculate is 20% wrong in the same direction, quietly, for years.

That is the whole job of this page. Measure once, carefully, and the number is done — the calculator keeps it, and the pool chemical calculator, the salt calculator and the cyanuric acid calculator start from it instead of asking you again. If you want the whole set in one place, the pool calculators hub lays out which one answers which question.

How Each Shape Is Worked Out

Three of the four shapes here are exact geometry, and one is an honest approximation:

Rectangle: length × width. No cleverness available or needed.
Round: π × (diameter ÷ 2)². This is the one where people accidentally double their pool by typing the diameter into two boxes, so the calculator only offers one.
Oval: π × (length ÷ 2) × (width ÷ 2) — the area of an ellipse. Above-ground “oval” pools are usually a rectangle with two half-circle ends rather than a true ellipse, which makes them hold a few percent more than this; if yours has straight sides, measuring it as a rectangle and adding the two end caps gets closer.
Kidney and freeform: 0.45 × (width A + width B) × length, where A is the widest point and B is across the narrow end. That factor is the approximation manufacturer volume worksheets print, and it lands slightly under a true double-ellipse. Being a shade low is the right direction for a number that sizes chemical doses.

Average Depth Is Where the Errors Live

Volume is surface area times average depth, and averaging the shallow end with the deep end is the convention every manufacturer chart uses. It is exact when the floor slopes evenly from one end to the other. It is generous when the pool has a long flat shallow section and then drops into a short deep hopper, because most of the floor is nowhere near that midpoint depth — on a pool like that, measure the depth at three or four points along the floor and average those instead.

The other common miss is measuring the wall rather than the water. A 52-inch above-ground wall does not hold 52 inches of water. Published charts — and the round table below — assume a 4 ft fill in that wall, which is 4 inches below the rail. Plenty of pools run closer to 6 inches down, and that alone is about 4% less water than the chart figure. Inches count here: a pool filled 3 inches lower than you assumed is about 6% smaller than the number you were dosing against, so measure the water line rather than reading a size off the box.

Gallons and Litres, Both, Always

Pool volume calculators tend to pick a side, which is unhelpful the moment your pool is in one country and your chemical label was printed in another. Every result here shows US gallons and litres together. A cubic meter is 1,000 litres, so a 8 × 4 m pool sloping from 1.2 m to 1.8 m averages 1.5 m and holds 48,000 litres — the number a European dosing label wants, since most of them are written per cubic meter or per 10,000 litres.

Common Pool Sizes, Already Worked Out

If your pool is a standard size, the two tables below already have it. They are computed by the same functions the calculator runs, so they cannot drift away from what the tool tells you. Anything non-standard — and every kidney and freeform pool — is what the calculator is for.

Round above-ground pools at 4 ft of water

Diameter	Surface area	US gallons	Litres
12 ft	113 sq ft	3,384	12,810
15 ft	177 sq ft	5,288	20,016
18 ft	254 sq ft	7,614	28,823
21 ft	346 sq ft	10,364	39,231
24 ft	452 sq ft	13,536	51,241
27 ft	573 sq ft	17,132	64,852
30 ft	707 sq ft	21,151	80,064

Water depth, not wall height — a 4 ft fill in a 52 in wall, which is the convention published above-ground charts use and sits 4 inches below the rail. A pool run nearer 6 inches down holds about 4% less than these rows. Every 3 inches of water you are out changes them by about 6%.

Rectangular inground pools, 3 ft to 6 ft

Size	Average depth	US gallons	Litres
24 × 12 ft	4.5 ft	9,695	36,699
28 × 14 ft	4.5 ft	13,196	49,951
30 × 15 ft	4.5 ft	15,148	57,342
32 × 16 ft	4.5 ft	17,235	65,242
36 × 18 ft	4.5 ft	21,813	82,572
40 × 20 ft	4.5 ft	26,930	101,941

Assumes an evenly sloping floor from 3 ft to 6 ft. A flat-bottomed pool of the same footprint at 4 ft holds 11% less.

How to calculate your pool volume

The shape decides which measurements you take — three for a round pool, five for a kidney. Two of them are always the depths at each end, which is where most wrong answers come from.

Pick the shape that matches your pool
Rectangle, round, oval, or kidney / freeform. The boxes change with the shape: a round pool is asked only for its diameter, and a kidney is asked for two widths — the widest point and the narrow end — because that is what its area estimate needs.
Set the ruler to feet or meters
Measure in whichever unit your tape uses. The answer always comes back in both US gallons and litres, so a metric measurement does not have to be converted first and an American pool still gets a litre figure for a chemical label printed in grams.
Measure the water, not the pool shell
Type the measurements your shape asks for, taken across the water surface — a diameter for a round pool, a length and width for a rectangle or oval, a length and two widths for a kidney — then the depth at the shallow end and at the deep end. For a flat-bottomed above-ground pool put the same number in both depth boxes, and use the real water line: most above-ground pools sit about 6 inches (15 cm) below the top rail.
Read the volume, then reuse it
The result updates as you type: gallons, litres, surface area and average depth. The volume is saved in your browser, so the chlorine, salt and cyanuric acid calculators on this site open with your pool already filled in.

Frequently Asked Questions

How many gallons is a 24 foot round pool?

A 24 ft round pool holding 4 ft of water is 13,536 US gallons, or 51,241 litres. Water depth is what moves that number, not the wall height: the same pool filled to 4 ft 6 in holds 15,228 gallons. Smaller round pools at 4 ft of water: 15 ft is 5,288 gallons, 18 ft is 7,614 gallons, and 27 ft is 17,132 gallons.

How do I calculate pool volume in litres?

Multiply the water surface area in square meters by the average depth in meters, then by 1,000 — a cubic meter is 1,000 litres. An 8 × 4 m pool sloping from 1.2 m to 1.8 m averages 1.5 m deep, so it holds 48,000 litres. The calculator above shows litres beside gallons on every result, which matters because most European chemical labels dose per cubic meter.

What average depth should I use?

Take the depth at the shallow end and the depth at the deep end and use the midpoint — a pool that runs 3 ft to 6 ft averages 4.5 ft. That is the convention every manufacturer volume chart uses, and it is exactly right when the floor slopes evenly the whole way. If your pool has a long flat shallow section and then drops into a short deep hopper, the true average is lower than the midpoint, so the figure comes out slightly generous. For dosing chemicals that is the wrong direction to be wrong in, so on a hopper-bottom pool measure the depth at three or four points along the floor and average those instead.

How do I work out the volume of a kidney or freeform pool?

Measure the length end to end, then two widths: across the widest point (A) and across the narrow end (B). The area is estimated as 0.45 × (A + B) × length, the approximation printed on manufacturer volume worksheets, and it runs a little under a true double-ellipse. For a freeform pool that is not really a kidney at all, take the two widest measurements you can find across it — the 0.45 factor absorbs a surprising amount of imprecision, and being a few percent low is the safe side when the number is about to size a dose of chlorine.

How many gallons is a 15 x 30 foot pool?

A 30 × 15 ft rectangular pool sloping from 3 ft to 6 ft averages 4.5 ft deep and holds 15,148 US gallons. The same pool with a flat 4 ft floor holds 13,465. Other common inground sizes at 3 to 6 ft: 24 × 12 is 9,695 gallons, 32 × 16 is 17,235 gallons, and 40 × 20 is 26,930 gallons.

Does the volume change if I do not fill the pool to the top?

Yes, and by more than people expect — volume is directly proportional to depth, so a pool filled 3 inches low holds roughly 6% less water than its rated size at a 4 ft depth. That is why this calculator asks for water depth rather than wall height. If you are dosing chemicals after a big splash-out or a partial drain, measure the water again rather than reusing the number on the box the pool came in.

Is a pool gallon calculator accurate enough to dose chemicals?

For a rectangle, a circle or an oval, the geometry is exact and the only error is in your tape measure — being 3 inches out on a 32 ft length changes the volume by under 1%. Freeform shapes are the approximate ones, and even there the estimate is comfortably inside the tolerance of pool dosing, where you add chemicals, circulate, and re-test rather than trusting a single calculation. The rule that matters more than precision: re-test before adding a second dose.

Do I need an account, and where does my pool data go?

No account, and nothing about your pool leaves your device. The calculation runs in your browser, and your measurements are saved in that browser only — which is also how the chlorine, salt and cyanuric acid calculators here can open with your volume already filled in.