Square 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.

Measurements:

1. Side Length (S) — the length of any one wall of the pool, measured inner surface to inner surface at the waterline. Before entering a value, confirm that at least two adjacent walls measure the same length.
2. Shallow End — water depth at the shallowest point, measured from the waterline to the pool floor. Do not measure from the deck or the top of the coping.
3. Deep End — water depth at the deepest point. For a flat-bottom pool, enter the same value as the Shallow End.

Results display in US gallons, litres, and cubic feet simultaneously. Use the volume for chemical dosing, pump sizing, heater selection, or water-change planning.

If you already know the exact surface area from a builder's plan or survey, expand the I Know My Pool's Surface Area panel below the main inputs and enter the area directly.

Most pools described as square are close to square rather than exact, so measuring at least two adjacent walls before calculating avoids using the wrong shape formula.

Square pool volume is the total amount of water the pool holds when filled to its normal waterline. It is measured in US gallons, litres, or cubic feet. The number depends on two measurements: the side length and the average water depth.

Accurate volume matters because chemical dosing, filtration pump sizing, heater capacity, and water-change scheduling all depend on how many gallons or litres are in the pool. Square pools are simpler to calculate than many other shapes — the surface area is just side × side — but only when all four walls are truly equal. If the walls differ, the pool is a rectangle and a rectangular pool calculator will give a more accurate result. The pool volume formula guide explains how surface area and depth combine across different shapes.

Square pools range from compact plunge-style installations at 10 ft per side to large inground designs at 24 ft per side or more. A small 10 × 10 ft square pool at 5 ft average depth holds about 3,740 gallons (14,158 L), while a 20 × 20 ft pool at the same depth holds 14,961 gallons (56,634 L) — roughly 4× more water.

Volume rises quickly with side length because the side is squared. Increasing the side from 16 ft to 20 ft — just 4 extra feet per wall — increases the surface area from 256 to 400 sq ft and adds more than 5,000 gallons (19,000 L) of water at 5 ft depth.

The most reliable approach is to measure the actual inside wall length at the waterline and enter that into the calculator. Outside dimensions from property surveys or deck plans overstate the water-holding area by several inches on each side.

Square pools use the simplest pool volume formula. Because the length and width are the same, the usual rectangular formula L × W × D simplifies to S × S × D — side length squared, times depth. A square pool is a special-case rectangle, so the same rectangular pool calculator would give identical results if you entered the same value for both length and width. Other pool shapes like octagons require shape-specific constants; the square does not.

Side × Side gives the water surface area in square feet. Squaring the side works because every square pool has four equal walls — length and width are the same number, so L × W becomes S × S. No shape factor is applied; the surface area is exact.

If the two wall measurements differ meaningfully — more than about 6 inches (15 cm) apart — the pool is rectangular and the rectangular pool volume calculator will be more accurate. Using the square formula in that case overstates or understates volume depending on which wall was measured.

Average depth is the midpoint of the shallow and deep end measurements: (Shallow + Deep) ÷ 2. Keep all measurements in the same unit — mixing feet and inches will produce an incorrect result.

A square pool with 16 ft sides, 3.5 ft shallow end, and 6.5 ft deep end:

This 16 ft square pool holds about 9,575 gallons (36,246 L). A 16 ft side is one of the most common residential square pool sizes, and knowing the exact volume helps the owner dose chemicals accurately and select the right pump capacity.

The correct measurement is from inner wall to inner wall along a straight wall at the waterline. Do not measure along the top of the coping, along the deck, or from corner to corner diagonally — the diagonal of a square is about 41 percent longer than the side, so using it would overstate the surface area dramatically.

Measure at least two adjacent walls to confirm the pool is truly square. If the two measurements differ by more than about 6 inches (15 cm), the pool is closer to a rectangle, and the rectangular pool volume calculator will give a more reliable volume by using separate length and width values.

Average depth is the midpoint of the shallow and deep end measurements: (Shallow + Deep) ÷ 2. Keep all measurements in the same unit — mixing feet and inches will produce an incorrect result.

Calculated using side length² × depth. 1 cu ft = 7.48052 US gal = 28.3168 L. Average depth = 5.0 ft unless noted otherwise. All four walls should be the same length. Use the rectangular pool calculator if they are not.

The smallest pool in this table holds 3,740 gallons (14,158 L), while the largest holds 21,544 gallons (81,552 L) — roughly 6× more water from a side length increase of only 14 ft. This rapid scaling is because the side length is squared: every additional foot of side length adds width and length simultaneously. For comparisons across different pool shapes, see the pool volume by size reference. For your specific dimensions, use the calculator above.

A 16 × 16 ft square pool at 5 ft average depth holds about 9,575 gallons (36,246 L). A 16 × 32 ft rectangular pool at the same depth holds about 19,150 gallons (72,491 L) — exactly double, because the rectangle's length is twice the square's side. Volume scales directly with surface area, so doubling one dimension doubles the water.

A small increase in side length on a square pool changes volume more quickly than the same increase on just one side of a rectangle. Increasing a 16 ft square to 18 ft per side adds 2,543 gallons (9,627 L), because both the length and width grow together. Adding 2 ft to only the length of a 16 × 16 ft rectangle (making it 18 × 16 ft) adds only 1,197 gallons (4,531 L).

If a pool is not truly square, the square formula can overstate or understate volume depending on which wall was measured and entered as S. A pool that measures 15 ft on one wall and 17 ft on the adjacent wall has a true surface area of 255 sq ft — not 225 (if 15 was entered) or 289 (if 17 was entered). For unequal walls, the rectangular pool calculator is the accurate choice.

Chlorine and other chemical doses are calculated by water volume. A 16 ft square pool holding 9,575 gallons (36,246 L) needs a different amount of chlorine than a 20 ft square pool holding 14,961 gallons (56,634 L). Overdosing can irritate skin and eyes; underdosing leaves the water undertreated. Always follow the product label and your pool equipment specifications for your exact pool setup. The chemical dosing guide explains volume-based calculations in detail.

Filtration pump sizing depends on total water volume. Most residential pools require the pump to turn over the full volume at least once every 6 to 8 hours. A 10,000-gallon (37,854 L) square pool needs a pump rated for at least 21 gallons per minute (GPM) to complete one turnover in 8 hours. An oversized pump wastes electricity; an undersized pump leads to poor circulation.

Heater and heat-pump sizing also depend on total volume. A pool heater rated for a 10,000-gallon pool will take noticeably longer to warm a 15,000-gallon pool. Knowing the true volume prevents undersized equipment and long heat-up times.

Water-change planning is simpler when the volume is known. A 10,000-gallon (37,854 L) pool at a typical garden hose flow rate of 10 gallons per minute takes roughly 17 hours to fill completely. Draining 25 percent for a seasonal refresh means replacing about 2,500 gallons (9,464 L). The pool volume formula guide covers how to plan these calculations across shapes.

1. Measuring only one wall and assuming all four are equal. Many pools described as "square" are slightly rectangular. Measuring just one wall and squaring it can overstate or understate the true surface area. Always measure at least two adjacent walls before using this calculator.

2. Using the diagonal instead of the wall length. The corner-to-corner diagonal of a square is about 41 percent longer than the side. Entering the diagonal as the side length would overstate the surface area by roughly double and inflate the calculated volume accordingly.

3. Measuring outside dimensions instead of inside water-holding dimensions. Coping, tile, and structural walls add inches on each side. The calculator needs the internal water dimension measured at the waterline, not the outside footprint from a site plan or property survey.

4. Mixing feet and inches incorrectly. A 16-foot side is 192 inches, not 16 inches. If the calculator expects feet, entering 192 would overstate the surface area by a factor of more than 140. Double-check whether your measurement is in feet, inches, or metres before entering a value.

5. Using a single depth point on a sloping floor. Many square pools slope from a shallow end to a deep end. Using only the deep-end measurement overstates water volume; using only the shallow end understates it. Enter both the shallow and deep measurements so the calculator can average them correctly.

6. Treating a slightly rectangular pool as square without checking. A pool that measures 15 ft on one wall and 17 ft on the adjacent wall has a real surface area of 255 sq ft. Entering 15 as the side gives 225 sq ft (12 percent low); entering 17 gives 289 sq ft (13 percent high). Use the rectangular calculator with separate length and width to avoid this error.