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Backyard pools are a great way to enjoy time outdoors with family and friends. But before you can jump in and have fun, you need to know how many gallons of water a pool holds. Knowing the size and capacity of a pool can help you determine the amount of water you will need for your swimming and other activities.

In this article, you will learn about the average pool size and its capacity, as well as tips to help you choose the right pool for your needs. So let’s begin!

Definition of a backyard pool

A backyard pool is an outdoor body of water used for recreational activities such as swimming, lounging, and playing. It tends to be relatively small in comparison to public pools. These pools typically come in two varieties – above-ground and inground.

Above-ground backyard pools are usually circular or rectangular structures that are prefabricated and require minimal installation time. These pools are generally a cheaper option than their inground equivalents and have become popular for those with smaller spaces or cost concerns.

Inground pools exist when hollowed out geological areas are filled with water. This can be achieved through shallow excavations or through deeper digging depending on the desired size of the pool. Common sizes range from 10 feet by 20 feet up to 20 feet by 40 feet, with depths varying between three and nine feet. Capacities in gallons depend on the size of the pool; shapes generally have little effect as capacity only correlates with area. Although custom shapes cannot be filled using a standard formula for calculations, a rough estimate of how many gallons any pool can contain requires knowing its dimensions in length, width, and depth in feet.

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Average Pool Sizes

Knowing the average pool sizes and their capacity is important before beginning any backyard pool project. The size of a pool can determine how many gallons of water it needs to hold, and this will determine how much water is necessary to fill the pool. Additionally, the size of a pool can also dictate how much time is necessary to maintain it.

Let’s take a look at the different pool sizes that are available, as well as their gallons capacity:

  • Small pools (8-10 feet in diameter) typically hold up to 5,000 gallons of water.
  • Medium pools (11-13 feet in diameter) typically hold up to 10,000 gallons of water.
  • Large pools (14-17 feet in diameter) typically hold up to 20,000 gallons of water.
  • Olympic-sized pools (18-21 feet in diameter) typically hold up to 40,000 gallons of water.

In-ground pools

In-ground pools come in a range of sizes, shapes and depths, and their capacity can range dramatically as a result. A standard rectangular in-ground pool is typically between 12 and 18 feet wide, with lengths ranging from 24 feet to 54 feet. However, more customized designs such as an L-shape, kidney shape or freeform are also available.

The depth of the pool can affect its capacity greatly – for example, a 12 X 24 in-ground pool can store 3,000 gallons of water if it is 48 inches deep. But the same size pool filled 5 feet deep can contain up to 21,000 gallons of water.

In general terms, most average sized in-ground pools will hold between 20k and 30k gallons of water when filled to their maximum capacity. This calculation considers the typical dimensions and depths mentioned above. However, you’ll need to measure your specific backyard pool so that you have an exact number for how many gallons it holds when filled to the maximum depth.

Above-ground pools

Above-ground pools are the most affordable option, though they require more maintenance. The most common sizes are 12-foot, 15-foot and 18-foot diameter round pools or oval pools up to 33 feet long. All above ground pools have a wall height of 48” and the shape of the pool is always round or oval.

An 18 foot diameter pool has a surface area of 254 square feet. With the wall height of 48”, the water capacity is 5,355 gallons when filled to within 1 inch from the top of the walls.

Similarly, a typical 15 foot diameter pool also has an approximate surface area of 178 square feet and a capacity of about 3,730 gallons when filled to within 1 inch from top of the walls. A 12 foot diameter pool has an approximate surface area of 113 square feet with a capacity of 2278 gallons when filled to within 1 inch from top of the walls.

Pool Capacity

The average pool size and how much water it can hold is an important factor to consider when planning to build a backyard pool. Knowing the pool capacity will help you determine how many gallons of water it needs to fill the pool completely, and how much water the pool can hold.

It is important to understand the capacity of the pool, since it affects the cost of installation, maintenance, and its overall usefulness. Below we will discuss the average pool size and its capacity.

How many gallons in a backyard pool

When determining pool capacity, it’s important to consider several factors, including size and shape of the pool as well as the type of pool filter and whether or not additional water features are included in the design. For example, a kidney-shaped pool has a different capacity than a rectangular one.

To calculate the volume of water that your swimming pool holds, simply measure its length, width and depth (shallow end through to the deep end) and multiply them together. Once you have this figure in cubic feet, multiply it by 7.48 to convert it into US gallons. There are also online calculators available to help with calculations if you don’t want to do manual calculations yourself.

The average backyard swimming pool is about 24′ x 12′ x 4′ deep, about 3/4 full at an estimated 6,400 US gallons of water when it’s filled. Some pools have concrete decks around them that add additional water depth making them hold up to 8–10 thousand gallons or more. In-ground pools can be used as both wading pools with shallow ends and as diving pools with deeper depths at their sides or center depending on design and shape.

Professional help may be required for big projects like calculating large public swimming pools containing more than 20,000 gallons but this will still be relatively simple for any experienced technician who can collect all the necessary information before beginning work on the project.

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Factors affecting pool capacity

Pool capacity is an important factor to consider in the selection of a new or existing pool. Many variables affect the capacity of the pool, possibly reducing the total volume from theoretical models. These factors include:

  • Size: length, width and depth
  • Shape: rectangle versus round pools
  • Surface area
  • Interior walls

Additionally, if water overflows from the pool for any reason, such as through a damaged liner or plumbing system, this can also reduce capacity.

The formula used to calculate average pool size will vary based on these variables as well as location and climate conditions of the area where the guide is being used. When selecting a new pool or evaluating an existing one, it’s essential to evaluate these factors in order to obtain an accurate understanding of how many gallons of water a given pool can hold. The precise practical capacity of most residential pools averages anywhere between 20,000-40,000 gallons or more depending on each individual situation. For reference though, a typical backyard oval-shaped swimming pool that measures 33×18 feet with 5 feet depth typically holds around 20,000 gallons of water when filled to its maximum limit.


After researching the size and capacity of pools, it has been determined that the average backyard pool is around 15,000 gallons. This will vary based on the type and size of the pool, as well as additional features that may be added.

However, on average, a 15,000-gallon capacity is the amount of water necessary to fill a pool that is:

  • 24 feet long
  • 12 feet wide
  • 5 feet deep

Benefits of knowing the pool capacity

Knowing the capacity of your pool can be useful for many reasons. For one, it allows you to accurately plan the amount of chemicals, water and other supplies needed for regular maintenance and repairs. Also, having an understanding of the average pool size and its capacity can help you save money on costly repairs by avoiding a situation where inadequate maintenance caused the pool to exceed its safe load limit. Finally, having an accurate estimate of a pool’s total content of water can help determine the number and size of pumps necessary to circulate all the liquid contained in the structure.

In addition to these practical benefits, knowing how many gallons are in a backyard pool gives homeowners peace of mind when inviting friends and family over for a dip!