How Many Gallons Is My Pool?

Step 1: Identify your pool shape

Almost every pool is one of four shapes: rectangle, oval, round, or kidney (freeform). The shape decides which multiplier you use, because a curved pool holds less water than a rectangle with the same overall length and width. If your pool is a freeform shape that is not quite a kidney, treat it as kidney: measure the longest length and the widest width, and accept that the answer is an estimate.

Above ground pools are nearly always round or oval, and the math below covers them too. The only difference is how you get the depth, which is step 2.

Step 2: Measure length, width, and average depth

Measure the length and width in feet with a tape measure, straight across the longest and widest points. For a round pool, you need only the diameter: the distance straight across the middle. Measuring across the waterline is fine; pool dimensions are usually quoted at the water surface.

Depth is where most people go wrong. You need the average depth, not the deep end. Add the shallow end depth to the deep end depth and divide by two. A pool that is 3 feet in the shallow end and 8 feet in the deep end has an average depth of 5.5 feet: (3 + 8) / 2 = 5.5.

For above ground pools, do not use the wall height as the depth. Water sits several inches below the top of the wall, so subtract about 6 to 8 inches from the wall height. A 52 inch wall holds about 4 feet of water. See above ground pool volume by size for a full chart.

Step 3: Multiply with the shape factor

Shape	Formula (feet)	Gives
Rectangle	Length x width x average depth x 7.48	Gallons
Oval	Length x width x average depth x 6.7	Gallons
Round	Diameter x diameter x average depth x 5.9	Gallons
Kidney / freeform	Length x width x average depth x 7.0	Gallons (estimate)

The 7.48 comes from the size of a cubic foot: one cubic foot of water is 7.48 gallons. The other multipliers shrink that number to account for curved walls. The math behind every multiplier is explained in how to calculate pool volume.

Worked examples

Example 1: rectangular inground pool. 32 feet long, 16 feet wide, 3 feet shallow, 8 feet deep. Average depth is (3 + 8) / 2 = 5.5 feet. Cubic feet: 32 x 16 x 5.5 = 2,816. Gallons: 2,816 x 7.48 = 21,065 gallons. That is a classic family-size inground pool.

Example 2: round above ground pool. 24 foot diameter, 4 feet of water depth. Gallons: 24 x 24 x 4 x 5.9 = 13,594 gallons. Note this uses the water depth, not the 52 inch wall height.

Example 3: kidney shaped pool. 28 feet long, 14 feet wide, average depth 4.5 feet. Gallons: 28 x 14 x 4.5 x 7.0 = 12,348 gallons. Because freeform shapes vary, treat this as an estimate and round up.

Quick reference: common pool sizes

Pool	Typical average depth	Gallons
12 x 24 ft rectangle	4.5 ft	9,695
16 x 32 ft rectangle	5 ft	19,150
18 x 36 ft rectangle	5.5 ft	26,661
20 x 40 ft rectangle	5.5 ft	32,914
24 ft round, above ground	4 ft water	13,594
15 x 30 ft oval, above ground	4 ft water	12,060

For a full breakdown of standard dimensions, see the pool size chart.

Why the gallon count matters

The gallon count is the starting point for nearly every pool task. Equipment like pumps, filters, and heaters is sized against the volume it has to move or heat. Anything added to the water, from salt systems to cleaning products, is measured against the volume it spreads through. And if you ever drain and refill, the water bill follows the gallon count directly. Measure once, write the number down, and keep it where you can find it.

Skip the hand math: the free pool volume calculator runs these exact formulas for all four shapes and also shows liters and water weight.