Calculators · Pool Volume Calculator

Measuring

Pool Volume Calculator

Pick your pool shape, type its size and depth and get the gallons of water, with liters and cubic feet too.

Length

Width

Bottom of the pool

The slope runs along the length (across the diameter in a round pool).

Depth

Water level below your depths

Optional. If the water surface sits below the depths you measured, type how far below. Empty counts as 0.

How to calculate pool volume

A pool holds its surface area times its average depth. That gives cubic feet, and each cubic foot holds 7.4805 US gallons. The number comes from the definition of the gallon. One US gallon is 231 cubic inches and one cubic foot is 12 × 12 × 12 = 1,728 cubic inches, so a cubic foot holds 1,728 ÷ 231 gallons. Measure everything in feet. The calculator also takes inches, meters and measurements like 32'6".

Shape	Cubic feet	Example
Rectangle	length × width × average depth	32 × 16 × 4 = 2,048 ft³ = 15,320 gal
Round	π ÷ 4 × diameter² × average depth	π ÷ 4 × 24² × 4 = 1,809.56 ft³ = 13,536 gal
Oval	π ÷ 4 × length × width × average depth	π ÷ 4 × 40 × 20 × 5 = 3,141.59 ft³ = 23,501 gal
L-shaped	(part 1 area + part 2 area) × depth	(20 × 10 + 10 × 8) × 5 = 1,400 ft³ = 10,473 gal

π ÷ 4 is about 0.7854. It is the share of its bounding rectangle that a circle or an oval fills, which is why a round or oval pool holds a little less than a rectangle of the same length and width.

Why 7.48 and not 7.5 gallons per cubic foot?

Swimmingpool.com, for example, uses 7.5 gallons per cubic foot (checked October 2026). It is an easy number to multiply, but it is rounded up. The exact value is 7.4805, so 7.5 adds about 0.26% to every result. For a 32 ft by 16 ft pool that is 4 ft deep, the exact figure is 15,320 gallons and the rounded one is 15,360. This calculator uses the exact value.

Average depth: when shallow plus deep divided by 2 works

The usual shortcut is (shallow end + deep end) ÷ 2. A 3 ft shallow end and an 8 ft deep end give (3 + 8) ÷ 2 = 5.5 ft. The shortcut is exact only if the floor slopes in one straight line from one end to the other. Swimmingpool.com says the same: it assumes a gradual and even slope, and suggests treating the pool as two parts when most of it is shallow and a small area drops off suddenly.

Many pools have a flat shallow end, a slope and a flat deep end. For those, pick “Flat shallow end, slope, flat deep end”. Type the two flat lengths and the calculator takes the slope as the rest of the pool. Each section counts for its own length:

40 ft long pool, 3 ft to 8 ft	Average depth	Gallons
Rectangle 16 ft wide, one straight slope	5.5 ft	26,331
Rectangle 16 ft wide, flat 20 ft + slope 10 ft + flat 10 ft	4.875 ft	23,339

Using 5.5 ft for the second pool would overstate its water by almost 13%. The average depth is (20 × 3 + 10 × 5.5 + 10 × 8) ÷ 40 = 4.875 ft, where 5.5 ft is the average depth of the 10 ft slope.

Round and oval pools with a sloped bottom

In a rectangle every slice across the width is the same size, so an average depth along the length is enough. An oval is narrow at the ends and wide in the middle, so the middle counts for more. The calculator cuts the oval into its sections and adds up the exact volume of each one. With one straight slope the result still equals the surface area times (shallow + deep) ÷ 2, because the two ends of the oval balance each other. With a flat section the simple average is not exact. A 40 ft by 20 ft oval with the same 20 ft, 10 ft and 10 ft profile holds 22,191 gallons, while multiplying its surface area by the length-weighted depth of 4.875 ft would give 22,913.

How many gallons is my pool? Common sizes

Rectangular pool	3 ft average	4 ft average	5 ft average
12 ft × 24 ft	6,463	8,618	10,772
15 ft × 30 ft	10,099	13,465	16,831
16 ft × 32 ft	11,490	15,320	19,150
20 ft × 40 ft	17,953	23,938	29,922

Round pool	3 ft average	4 ft average	5 ft average
15 ft across	3,966	5,288	6,610
18 ft across	5,711	7,614	9,518
21 ft across	7,773	10,364	12,955
24 ft across	10,152	13,536	16,921
27 ft across	12,849	17,132	21,415

A 40 ft by 20 ft pool is the same as a 20 ft by 40 ft pool. Length and width can be swapped. If your depth is not in the table, the gallons scale with it: a pool that is 4.5 ft deep holds 4.5 ÷ 4 of the 4 ft figure.

Use the real water depth

Water is not always as deep as the pool. Swimmingpool.com points out that its example hot tub is 4 ft deep but is filled to about 3 ft, and that using 4 ft would overstate the water by 33%. If you measured the depth of the pool itself and the water sits lower, type the gap in the box “Water level below your depths”. The calculator takes it off every depth. It stops with a message if the water would not cover the whole floor, because a floor that sticks out of the water is a different shape.

What this calculator assumes

Vertical walls. Steps, benches, swim-outs, sumps and coved corners are not subtracted or added. If a large part of the pool is a bench or a step, measure it as its own rectangle.
A floor made of straight sections. The slope runs along the length. A pool that also slopes across its width is not covered.
Kidney and free-form pools. They have no exact formula here. Split the outline into a few rectangles, circles and ovals, calculate each one and add the gallons. The result is an estimate.
US gallons. One US gallon is 3.7854 liters. Imperial gallons, used in the UK, are larger and are not shown.
Shallow end of zero. A beach entry that starts at 0 ft works. Type 0 in the shallow end depth.

Gallons, liters, cubic feet and cubic meters

One unit	US gallons	Liters	Cubic feet
1 cubic foot	7.4805	28.3168	1
1 cubic yard	201.97	764.55	27
1 cubic meter	264.17	1,000	35.3147

To convert other volumes or find the cubic feet of other shapes, use the cubic feet calculator or the cubic yard calculator.

The volume in gallons is the number that pool products, pumps and covers ask for. This page does not give chemical doses or run times. Follow the label of each product, which tells you how much to use for your gallons.

Frequently asked questions

How do I calculate how many gallons are in my pool?

Find the volume in cubic feet, then multiply by 7.4805. For a rectangular pool, multiply length by width by average depth, all in feet. A 32 ft by 16 ft pool with an average depth of 4 ft holds 32 × 16 × 4 = 2,048 cubic feet, which is 2,048 × 7.4805 = 15,320 gallons.

How many gallons is a 16x32 pool?

It depends on the depth. A 16 ft by 32 ft rectangular pool with an average depth of 3 ft holds about 11,490 gallons. At 4 ft it holds about 15,320 gallons and at 5 ft about 19,150 gallons.

How many gallons is a 12x24, 15x30 or 20x40 pool?

At an average depth of 4 ft, a rectangular 12 ft by 24 ft pool holds about 8,618 gallons, a 15 ft by 30 ft pool about 13,465 gallons and a 20 ft by 40 ft pool (the same as 40x20) about 23,938 gallons. Change the depth and the gallons change in the same proportion, so enter your own depth in the calculator.

How do I find the average depth of a pool with a shallow and a deep end?

Add the shallow end depth and the deep end depth and divide by 2, but only if the floor slopes in one straight line from end to end. If the pool has a flat shallow section, a slope and a flat deep section, pick the flat-slope-flat option. The calculator weights each section by its length. A 40 ft by 16 ft pool that is 3 ft deep for 20 ft, slopes for 10 ft and is 8 ft deep for the last 10 ft has an average depth of 4.875 ft, not 5.5 ft.

How do I calculate the volume of a round pool?

Multiply π ÷ 4 by the diameter squared and by the average depth, all in feet, then multiply by 7.4805 for gallons. A round pool 24 ft across and 4 ft deep holds π ÷ 4 × 24 × 24 × 4 = 1,809.56 cubic feet, which is 13,536 gallons.

How do I calculate the volume of an oval pool?

Multiply π ÷ 4 (about 0.7854) by the length, the width and the average depth, all in feet. An oval pool 40 ft long, 20 ft wide and 5 ft deep holds π ÷ 4 × 40 × 20 × 5 = 3,141.59 cubic feet, which is 23,501 gallons. This is the exact formula for an ellipse.

Why does this calculator use 7.48 gallons per cubic foot and not 7.5?

A US gallon is defined as 231 cubic inches and a cubic foot is 1,728 cubic inches, so a cubic foot holds 1,728 ÷ 231 = 7.4805 gallons. Some pool sites round this to 7.5, which makes every result about 0.26% higher. For a 32 ft by 16 ft pool that is 4 ft deep, 7.5 gives 15,360 gallons instead of 15,320.

How many liters of water does a pool hold?

Multiply the gallons by 3.7854 or the cubic feet by 28.3168. The calculator shows the liters for you. A pool of 15,320 gallons holds about 57,993 liters, which is 57.99 cubic meters.