What is the formula for pool gallons?

For a round pool, multiply the diameter in feet by itself, then by the average water depth in feet, then by 5.9. For a rectangle, multiply length by width by average depth by 7.5. For an oval, multiply length by width by average depth by 5.9. The 7.5 figure is the number of gallons in a cubic foot, and the 5.9 figure folds in the ratio of a circle to its bounding square, so you can use the diameter directly rather than calculating the radius.

Should I use the wall height or the water depth?

Water depth, always. Above ground pools are filled to roughly 6 inches below the top rail so the skimmer sits at the correct level, so a 52 inch wall holds about 46 to 48 inches of water. Using the wall height instead overstates volume by about 10 percent, which is enough to under-dose chlorine and shock noticeably. Measure the actual depth with a pole marked in inches rather than assuming.

How much does it cost to fill a 15 foot pool?

At around 4,400 gallons for a 48 inch pool and typical US municipal water and sewer rates as of 2026, expect roughly $25 to $70 on city water, with wide regional variation. Ask your utility whether they offer a pool fill credit that waives the sewer charge, since sewer is often the larger half of the bill and the water never enters the sewer. Water delivery by truck runs considerably more, generally $200 to $400 for that volume depending on distance.

Does the volume change how much chlorine I add?

Directly, because every chemical dose is calculated per gallon. Getting the volume wrong by 10 percent means every shock, every algaecide dose and every pH adjustment is off by the same margin, and repeated over-dosing of chlorine drives up cyanuric acid and stabilizer levels over a season. Write your calculated volume on the filter housing or inside the equipment cover so you dose from a number rather than from memory.

How long does it take to fill a 15 foot pool with a garden hose?

Roughly 6 to 10 hours for 4,400 gallons at a typical garden hose flow of 8 to 12 gallons per minute, though well water and low-pressure supplies can take considerably longer. Two hoses roughly halve it. Do not leave a filling pool unattended overnight, and keep an eye on the level as it approaches the skimmer, because overfilling an above ground pool puts load on the top rails and floods the skimmer mouth.

How Many Gallons in a 15 Foot Above Ground Pool?

Written & researched by Derek Holt Home & Appliances Editor

Updated October 2026

Wide view of a person skimming leaves from the surface of a backyard pool, in warm late-afternoon light

Affiliate Disclosure

Some links on this page are affiliate links. As an Amazon Associate, we earn from qualifying purchases — at no extra cost to you. We do not buy, test, or physically handle the products we cover; our rankings come from aggregated owner reviews, ratings and expert consensus. Commissions never change our verdicts. How we rank · full disclosure.

A 15 foot round above ground pool holds about 3,700 gallons at 42 inches of water depth, 4,400 gallons at 48 inches, and 5,000 gallons at 52 inches. Those figures use actual water depth, not wall height — above ground pools are filled to roughly 6 inches below the top rail so the skimmer sits correctly, so a 52 inch wall holds about 46 to 48 inches of water. The formula for any round pool is diameter in feet, times diameter, times average depth in feet, times 5.9.

What does a 15 foot pool hold at each depth?

Wall height is what the pool is sold as; water depth is what determines chemical dosing and turnover. The middle column below is the one to use in practice.

Wall height	Typical water depth	Gallons
36 in	30 in	~3,300
42 in	36 in	~3,700
48 in	42 in	~4,400
52 in	46 in	~5,000
54 in	48 in	~5,300

Manufacturer literature often quotes a higher number because it assumes filling to 90 percent of wall height or to the rim. Owners consistently find the real filled volume is several hundred gallons below the box figure, which matters when you are dosing shock.

Low-angle view of a person skimming leaves from the surface of a backyard pool, in bright midday sun

How do I calculate it for any pool?

Three formulas cover almost every backyard pool. All of them return US gallons and all of them use feet.

Shape	Formula	Example
Round	Diameter × Diameter × Avg depth × 5.9	15 × 15 × 3.5 × 5.9 = 4,646
Oval	Length × Width × Avg depth × 5.9	18 × 12 × 3.5 × 5.9 = 4,460
Rectangle	Length × Width × Avg depth × 7.5	16 × 32 × 5 × 7.5 = 19,200
Variable depth	Average the shallow and deep ends first	(3 + 8) ÷ 2 = 5.5 ft average

The 7.5 in the rectangle formula is simply the number of gallons in a cubic foot, 7.48 rounded. The 5.9 used for round and oval pools folds in the ratio of a circle to its bounding square, which is why you can plug the diameter straight in without halving it for a radius.

Golden-hour view of a person skimming leaves from the surface of a backyard pool

Why does getting the volume right matter?

Every decision downstream is per-gallon. Chlorine, shock, algaecide, stabilizer, pH adjusters and clarifier are all dosed by volume, so a 10 percent error compounds through the season. Chronic over-dosing of stabilized chlorine in particular raises cyanuric acid, which locks up free chlorine and produces the frustrating situation of a high test reading with no sanitizing power — the mechanism is covered in why a pool keeps losing chlorine, and target ranges in what pool pH and chlorine levels should be.

Volume also sets the pump and filter you need, because turnover is defined as one complete pass of the pool volume through the filter. A 4,400 gallon pool needs only about 9 GPM for an eight-hour turnover, which is why oversized pumps are so common on small above ground pools — see what size pool pump you need. And it drives heating time and cost, since heating any body of water is a straight function of gallons and the temperature rise.

Close-up detail of the material being worked in a pools & spas project, in warm late-afternoon light

What about other common above ground sizes?

The same formula gives the whole range. These figures assume the pool is filled to the normal level, about 6 inches below the top rail.

Pool size	48 in wall	52 in wall
12 ft round	~2,800 gal	~3,200 gal
15 ft round	~4,400 gal	~5,000 gal
18 ft round	~6,400 gal	~7,300 gal
21 ft round	~8,700 gal	~9,900 gal
24 ft round	~11,400 gal	~13,000 gal
27 ft round	~14,500 gal	~16,400 gal
15 × 30 ft oval	~9,300 gal	~10,600 gal

For the 24 foot case in detail, including how liner shape and cove depth shift the number, see how many gallons a 24 foot round pool holds. Filling costs and the sewer credit question are covered in how much it costs to fill a pool with water, and pool selection in best above ground pools.

We never buy, test or physically handle the products we rank. Recommendations come from aggregated owner reviews, star ratings, review volume and expert consensus — see how we rank.

More from this hub: Pools & Spas · Best above ground pools · Leaving a pool up all year · How we rank