Round Pool Volume Calculator

Select Imperial or Metric at the top of the input panel. Imperial shows results in US gallons and cubic feet; Metric shows litres and cubic metres.

Enter your pool dimensions:

1. Diameter (D) — the distance from inner wall to inner wall, measured straight across the pool through the centre. Enter the full diameter, not the radius. If you enter the radius by mistake, the result will be one quarter of the true volume because the formula squares this value.
2. Shallow End (D₁) — the water depth at the shallowest point, measured from the waterline straight down to the pool floor. In above-ground round pools, water depth is not the same as wall height — most pools are filled several inches below the top rail.
3. Deep End (D₂) — the water depth at the deepest point. For a flat-bottom above-ground pool, enter the same value as the Shallow End. The calculator averages both depths automatically.

Results display in US gallons, litres, and cubic feet simultaneously. Use the volume for chemical dosing, pump sizing, salt-system setup, and refill planning.

In many Intex and Bestway round pools, the listed diameter refers to the overall frame or wall span, while the internal waterline diameter is typically 4 to 8 inches smaller.

Round pool volume is the total amount of water the pool holds when filled to its normal waterline. It is expressed in US gallons, litres, or cubic feet. The number depends on two measurements: the internal diameter of the circle and the average water depth.

Knowing the exact volume matters because chlorine dosing, pump sizing, salt-system calibration, and water-change scheduling all depend on how many gallons or litres are in the pool. Round pools are one of the most precise pool shapes to calculate because the water surface forms a true circle, and the cylinder formula — circle area times depth — maps it exactly without shape-factor guesswork.

Round pools range from compact 10 ft above-ground models to large 33 ft in-ground installations. The most common above-ground diameters sold by Intex, Bestway, and similar brands are 12, 15, 18, 21, 24, and 27 ft. A 12 ft round pool at 3.83 ft water depth holds about 3,240 gallons (12,266 L), while a 27 ft pool at the same depth holds 16,403 gallons (62,093 L) — roughly five times more water from a diameter increase of only 15 ft.

Two round pools with the same diameter can still hold different volumes if the water depth differs. An 18 ft pool at 3.5 ft depth holds 6,662 gallons (25,220 L), but the same pool at 5.0 ft depth holds 9,518 gallons (36,029 L) — a 43 percent increase from just 1.5 extra feet of water.

Above-ground round pools almost always have shallower water than similarly sized in-ground round pools because they have flat bottoms and are filled below the top rail. In-ground pools often have a sloped floor with a deep end of 5 to 8 ft, which raises the average depth and total volume considerably.

Capacity should always be estimated from the internal water dimensions — the diameter measured inner wall to inner wall, and the actual water depth — not from packaging labels or outer-rim measurements.

A round pool is a cylinder: the water fills a circular cross-section to a uniform or averaged depth. Calculating its volume means finding the area of the circle and multiplying by the water depth. This is geometrically exact — unlike oval pools or freeform shapes that need approximation constants, a circle's area is precisely π × radius². The same formula applies to above-ground round pools of any brand.

Diameter squared (D²) gives the area of a square that encloses the circle. The π/4 factor (0.7854) trims that square down to the actual circular area. This is mathematically identical to π × radius² because (D/2)² × π = D² × π/4. The radius is half the diameter, and squaring it means that a pool twice as wide holds four times the surface area — volume scales with the square of the diameter, not linearly.

Entering the radius into the diameter field produces a result that is exactly one quarter of the correct volume. A 24 ft pool entered as 12 (the radius) would show about 3,240 gallons instead of the true 12,961 gallons at 3.83 ft depth. Always enter the full wall-to-wall diameter.

Average depth equals (Shallow End + Deep End) ÷ 2. Keep all measurements in the same unit — mixing feet and metres produces an incorrect result. The pool volume formula guide covers how this calculation works across different pool shapes.

A 24 ft round above-ground pool with a 52-inch wall, filled to a practical water depth of 3.83 ft (about 46 inches — several inches below the top rail):

A 24 ft round pool is one of the most common family above-ground sizes. Getting the internal diameter and actual water depth right matters — using the wall height (4.33 ft) instead of the true water depth (3.83 ft) would overstate this pool's volume by roughly 1,700 gallons (6,400 L).

Stretch a tape measure from inner wall to inner wall at the waterline, passing through the exact centre of the circular pool. This straight-line distance is the diameter — the longest width across the circle. Measure at least twice at different angles and use the average.

Do not measure the outside frame, upper rail, or rely on packaging sizes if the actual internal water diameter is smaller. In many above-ground round pools, the advertised diameter describes the full frame or wall span, while the internal waterline diameter is 4 to 8 inches less.

Water depth is the distance from the waterline straight down to the pool floor. Use a marked pole or weighted tape and take the reading at the shallowest and deepest points.

Wall height and water depth are not the same in most above-ground round pools. A 52-inch (4.33 ft) wall is typically filled only to about 46 inches (3.83 ft) because the waterline sits below the top rail. Using wall height instead of water depth overstates the volume — on a 24 ft pool, that difference alone adds roughly 1,700 gallons (6,400 L) to the estimate.

Calculated using circle area × water depth. Diameter is measured inner wall to inner wall through the centre. Use actual water depth, not wall height. Depth columns: 3.5 ft = common practical fill level for smaller above-ground pools; 3.83 ft = common practical water depth for 52-inch wall above-ground pools; 5.0 ft = common deeper round-pool reference. Conversion factors follow the calculator's source logic.

The smallest pool in this table holds 2,056 gallons (7,784 L) and the largest holds 31,990 gallons (121,097 L) — a 15× range from a diameter increase of only 23 ft. Diameter changes volume quickly because the radius is squared: each additional foot of diameter adds water in both directions across the circle. For above-ground models in the 12–27 ft range, see the above-ground pool volume calculator. For comparisons across different pool shapes, see the pool volume by size reference. For any size not listed, use the calculator above with your exact measurements.

Above-ground pools account for the majority of round pool volume searches because brands like Intex and Bestway sell millions of round frame and inflatable-ring pools each year. Standard sizes include 12, 15, 18, 21, 24, and 27 ft — all matching the reference table above. The above-ground pool volume calculator handles both round and oval above-ground shapes on a single page.

Wall height and water depth differ in every above-ground pool. A 48-inch (4 ft) wall holds water to roughly 44 inches (3.67 ft), and a 52-inch (4.33 ft) wall holds water to about 46 inches (3.83 ft). The gap comes from filling several inches below the top rail to prevent surge and wave overflow. Use the actual water depth — not the wall height printed in the spec sheet — when calculating volume.

If the pool owner is unsure of the exact internal diameter, checking the model number on the manufacturer's website usually gives both the outer frame dimension and the internal water diameter. For Intex Ultra XTR and Bestway Power Steel models, the internal diameter is typically 4 to 6 inches less than the marketed size per side.

Chlorine and other treatment chemicals are dosed by water volume. A 15 ft round pool holding 5,063 gallons (19,165 L) needs a different amount than an 18 ft pool holding 7,291 gallons (27,598 L). Underdosing leaves the water undertreated; overdosing can irritate skin and eyes. Always follow the product label and your equipment specifications for your exact pool setup. The chemical dosing guide explains volume-based calculations in detail.

Filtration pump and filter sizing depend on total water volume. Most residential pools require the pump to turn over the full volume at least once every 6 to 8 hours. An 18 ft round pool at 7,291 gallons needs a pump rated for at least 15 gallons per minute (GPM) to complete one turnover in 8 hours. An oversized pump wastes electricity; an undersized pump leads to poor circulation and cloudy water.

Salt-water chlorine generators are rated by pool volume. A unit rated for 15,000 gallons will struggle to keep chlorine levels stable in a 24 ft pool holding close to 13,000 gallons if the actual volume was underestimated during installation. Accurate volume measurement at setup prevents ongoing chlorine shortfall.

Refill and partial-drain planning is easier when the true volume is known. A 24 ft pool holding 12,961 gallons (49,063 L) at a typical garden hose flow rate of 10 gallons per minute takes over 21 hours to fill from empty. Draining 25 percent for a seasonal refresh means replacing about 3,240 gallons (12,266 L). Round pools are straightforward to calculate only when diameter and water depth are measured correctly.

1. Entering radius instead of diameter. The calculator's input field is labelled DIAMETER (D). If you enter the radius (half the diameter) by mistake, the formula squares that value and the result is exactly one quarter of the true volume. A 24 ft pool entered as 12 would show roughly 3,240 gallons instead of 12,961 gallons at 3.83 ft depth.

2. Measuring the outside frame instead of the internal waterline. Many Intex and Bestway round pools have a marketed size that describes the outer frame or top-rail span. The internal water diameter is typically 4 to 8 inches smaller. A pool sold as 18 ft that measures 17 ft 4 in inside holds about 7 percent less water than the 18 ft figure would give in the formula.

3. Using wall height instead of water depth. A 52-inch wall pool is not filled to 52 inches. Water depth is usually 4 to 6 inches less because the waterline sits below the top rail. On a 24 ft pool, that difference overstates volume by about 1,700 gallons (6,400 L).

4. Assuming all pools of the same diameter hold the same volume. A 24 ft pool at 3.5 ft water depth holds 11,844 gallons (44,836 L), while the same diameter at 5.0 ft depth holds 16,921 gallons (64,051 L). Depth is just as important as diameter when estimating volume.

5. Mixing feet and inches incorrectly. A 24-foot diameter is 288 inches, not 24 inches. If the calculator expects feet, entering 288 would overstate volume by a factor of 144. Confirm whether your measurement is in feet, inches, or metres before entering a value.

6. Copying brand-stated capacity without matching the actual fill level. Manufacturer spec sheets sometimes list volume at maximum wall height. If the pool is filled only to 3.83 ft instead of the full 4.33 ft wall, the actual volume is about 12 percent less than the brand figure. Always calculate from your real water depth.