How Many Gallons Is My Pool? Easy Formulas and Common Sizes

Published October 30, 2026 · A Clear Alternative Water, Pennsauken NJ, since 1991

To find how many gallons your pool holds, measure the water's length, width and average depth in feet, multiply them together, and then multiply by 7.5 for a rectangular pool or 5.9 for a round or oval pool. A 16 by 32 foot in-ground pool with an average depth of 5 feet holds about 19,200 gallons. A 24-foot round above-ground pool filled to 4 feet holds about 13,600 gallons. Knowing your number helps you dose chemicals correctly, size equipment and know how many truckloads it takes to fill. A Clear Alternative delivers pool water across eight South Jersey counties; call 856-856-5210 any time.

Why Your Pool's Volume Matters

• Chemical dosing. Every chlorine, shock, pH and alkalinity instruction is written per a certain number of gallons. Guessing too low leads to over-treating; guessing high leaves the water under-treated.
• Equipment sizing. Pumps, filters, heaters and salt systems are rated by pool volume and turnover time.
• Filling and refilling. Our tanker carries 6,200 gallons, so your volume tells you how many loads a fill takes.
• Draining and partial refills. When you lower the water to dilute high stabilizer or calcium, you need to know how much is coming out and going back in.

How to Measure Your Pool

1. Measure in feet. Use a long tape. Convert inches to decimal feet: 6 inches is 0.5 feet, 3 inches is 0.25 feet.
2. Measure the water, not the deck. Length and width are measured wall to wall at the water line.
3. Find the average depth. Measure the depth of the water at the shallow end and the deep end, add them, and divide by 2. A pool that is 3.5 feet at the shallow end and 8 feet at the deep end averages 5.75 feet. If the pool has a long shallow section and a short deep hopper, the true average is a little lower than that simple math; nudge the number down.
4. Use the water level, not the wall height. Water usually sits several inches below the top of an above-ground wall and halfway up the skimmer on an in-ground pool.

Pool Volume Formulas by Shape

One cubic foot holds about 7.48 gallons, which the pool industry rounds to 7.5. The other multipliers fold in the geometry of curved shapes. These are the same formulas published by SwimmingPool.com and in Pentair's engineering data.

Rectangle or Square

Length x width x average depth x 7.5 = gallons. Example: 18 x 36 feet at 5 feet average depth = 24,300 gallons.

Round

Diameter x diameter x average depth x 5.9 = gallons. Example: an 18-foot round pool with 4 feet of water = about 7,650 gallons.

Oval

Length x width x average depth x 5.9 = gallons. Example: a 15 by 30 foot oval with 4 feet of water = about 10,600 gallons. Many above-ground ovals have straight sides with rounded ends; for those, this formula comes out slightly low.

Kidney

(Width A + width B) x length x 0.45 x average depth x 7.5 = gallons. Width A and width B are the widest points of the two lobes. Example: lobes of 10 and 16 feet, 32 feet long, 5 feet average depth = about 14,000 gallons.

Freeform and L-Shaped Pools

Split the pool into simple rectangles and circles, work out each section, and add them. An L-shaped pool is two rectangles. A lagoon shape is usually close enough when treated as an oval and reduced by about 10 percent.

Common Pool Sizes and Their Gallons

Round Above-Ground Pools

Based on typical water depths (about 3.5 feet in a 48-inch wall and about 4 feet in a 52 or 54-inch wall):

• 15-foot round, 48-inch wall: about 4,650 gallons (one load)
• 18-foot round, 52-inch wall: about 7,650 gallons (just over one load)
• 21-foot round, 52-inch wall: about 10,400 gallons (two loads)
• 24-foot round, 52-inch wall: about 13,600 gallons (just over two loads)
• 27-foot round, 52-inch wall: about 17,200 gallons (three loads)

Rectangular In-Ground Pools

• 15 x 30 feet, 3.5 feet average (sport pool): about 11,800 gallons (two loads)
• 16 x 32 feet, 5 feet average: about 19,200 gallons (just over three loads)
• 18 x 36 feet, 5 feet average: about 24,300 gallons (about four loads)
• 20 x 40 feet, 5.5 feet average: about 33,000 gallons (five loads plus a top-off)

Load counts assume the pool is empty and our standard 6,200-gallon tanker; "just over" means the last load is partly used. If the pool is partly full, the remaining amount is what matters. Your exact number depends on your real water depth, so measure your own pool before ordering.

Hot Tubs and Spas

Most home hot tubs hold a few hundred gallons; the manufacturer's manual or the label near the control panel lists the number. Because the shape is full of seats and footwells, the formulas above overestimate. Our hot tub water delivery page explains how a spa fill works.

Other Ways to Check Your Number

• Paperwork. The builder's plans, liner order form, or the box from an above-ground kit often lists the capacity.
• A water meter reading. If you have filled from a metered supply before, the before-and-after reading shows how much went in.
• Your last delivery. If we filled your pool before, we can tell you how many loads it took.

Turning Gallons Into a Delivery Plan

Once you know your volume, ordering is simple. Tell us the pool size and shape, how much water is in it now, and how the truck reaches the yard. Our guide to how buying pool water by truck works covers delivery day, and our pool fill page explains our service. For new above-ground pools, see above-ground pool water delivery.

Serving Eight South Jersey Counties

We deliver pool water to homes, swim clubs and builders in Burlington, Camden, Gloucester, Atlantic, Salem, Cape May, Mercer and Monmouth counties. See our service areas for towns we serve.

When to Call A Clear Alternative

Call us when you are filling a new pool, refilling after a drain or liner change, or topping up a pool that lost a lot of water over the winter. Not sure of your gallons? Give us the shape and measurements and we will help you work out how many loads you need. A Clear Alternative is a family-run company that has served South Jersey since 1991 from 9230 Collins Ave in Pennsauken. Call 856-856-5210 any time, call our office at 856-663-8088, or request a quote online.

Frequently Asked Questions

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

Multiply length, width and average depth in feet, then multiply by 7.5 for a rectangular pool or 5.9 for a round or oval pool. Average depth is the shallow end depth plus the deep end depth, divided by 2.

How many gallons is a 24-foot round above-ground pool?

About 13,600 gallons with 4 feet of water, which is typical for a 52 or 54-inch wall. That is just over two loads from our 6,200-gallon tanker.

How many gallons is a 16 by 32 in-ground pool?

About 19,200 gallons at a 5-foot average depth. Shallower or deeper pools hold proportionally less or more.

Why is the round pool multiplier 5.9 instead of 7.5?

A circle covers about 78.5 percent of the square around it. 7.48 gallons per cubic foot times 0.785 is about 5.9, so the shortcut uses diameter times diameter instead of the radius formula.

How many truckloads does it take to fill my pool?

Divide your pool's gallons by 6,200 and round up. Most above-ground pools take one to three loads, and most residential in-ground pools take two to six.

Do I measure to the top of the wall?

No. Measure to the actual water line. Water usually sits several inches below the top of an above-ground wall.