Average Swimming Pool Size in Gallons

A typical family inground pool holds roughly 10,000 to 18,000 gallons. That is a range, not a single number, because “average” depends on which pools you count. Add above ground pools to the sample and the average drops sharply. Change the shape of the floor and the same footprint can hold a few thousand gallons more or less.

Why there is no single average

The US has two very different kinds of backyard pool in large numbers. Pool Magazine puts the installed base at roughly 5.4 million inground pools against 3.4 million above ground. That makes above ground pools about 39% of the total (3.4 / 8.8 = 0.386). An average that leaves them out describes one market. An average that includes them describes a blend of two, and the blend sits far below a typical inground pool.

So when you see an “average pool size” figure, the first question is what went into it. Most figures you will find online describe inground pools only, usually from a builder.

What builders say is typical for inground pools

Sheller Outdoor Living, a pool builder, says “the most common dimensions we install for families fall between 14×28 and 16×32 feet.” It gives 3 to 4 feet in the shallow end and 5 to 6 feet in the deep area, and says an “average” family pool “usually falls between 10,000 and 18,000 gallons”.

Those figures hold up when you run them. Take the midpoint of the depth ranges, 4.5 feet, and use the rectangle formula from our pool volume hub: length x width x average depth x 7.5.

Both land inside the builder’s 10,000 to 18,000 range. And 17,280 matches PoolAndSpa.com’s published 16 x 32 figure exactly. Two independent sources agree on that size.

One small wrinkle. Sheller pairs its gallon range with 400 to 600 square feet of surface area, but a 14 x 28 is 392 square feet, just under its own floor. It does not change the answer. It does show that even a builder’s round numbers are round.

For another reference point, HomeGuide’s salt pool cost article prices salt for “an average 18,000 gallon pool”, the top of the builder’s range.

How wide the real spread is

Typical is not the same as common to everyone. PoolAndSpa.com’s rectangular inground chart shows how far sizes run:

A small pool at its shallowest and a large pool at its deepest are almost eight times apart. Depth alone moves a 12 x 24 by half again. An average sitting in the middle of that spread tells you very little about any one backyard.

The average depth trap

The 4.5 foot figure above assumes the floor slopes evenly from 3 feet to 6 feet. Most pools do not. Many have a long flat shallow end, a steep break, and a short deep section.

Our pool volume hub works a real 16 x 32 of that shape. Weighted properly by how much of the floor sits at each depth, it comes to 17,593 gallons. Averaged naively, shallowest plus deepest divided by two, it comes to 20,106. That naive figure overstates the water by 14%.

Same footprint, same shallow and deep numbers, and the answer moves by more than 2,500 gallons because of the floor. So even a correct “average pool” number can be wrong for your pool by the shape of what is under the water.

You can tell which case you are in with a tape measure and a pole. Measure the depth at the shallow wall, at the point where the floor starts to drop, and at the deepest spot. Then measure how far along the pool each of those sections runs. If most of the length sits at the shallow depth, a simple average of shallow and deep will overstate your water. If the floor slopes in one even line from end to end, the simple average is close. Either way, the lengths of each section are what the calculator needs, and they are what separate your pool from the average.

Above ground pools are a different scale

Above ground pools run much smaller, and their gallon charts carry their own problem: most assume the pool is filled to the top of the wall. For sizes and figures at a realistic fill line, see how many gallons is an above ground pool. That page covers round and oval sizes with both common depth assumptions.

Why an average is useless for dosing

Everything you add to a pool is dosed by gallons. Salt, acid, stabilizer and shock all scale with volume. If you dose a 13,000 gallon pool as if it were an 18,000 gallon “average”, you add about 38% too much of everything (18,000 / 13,000 = 1.38). In a salt pool that matters most, because salt does not get used up and only leaves with water through backwashing, splashing or draining.

Gallons also decide the size of the salt cell you need, which is covered in what size salt cell do I need, and they sit behind every step of routine salt water pool maintenance.

Use the averages here to sanity check a number, not to replace one. Measure your length, width and depths, note where the floor breaks, and run them through the pool volume calculator. If you have ever wondered how many gallons is my pool, that is the only answer worth dosing from. Then run that number through the salt calculator for your pool’s volume instead of dosing from an average.

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