In order to figure out the number of chemicals your pool needs, you need to determine how many gallons of water it holds. To do that, you need to use a “tape measure” to determine the Length, Width, and Average depth. Then some good old Math.

So here are the formulas to calculate how much water is in your swimming pool:

These formulas hold true for both In-ground as well as above-ground pools.

**Rectangular, Square or Free Form Pools**

Length x Width x Average Depth x 7.5 = Total gallons

For example: 16′ x 32′ x 4.5′ x 7.5 = 17,280 Gallons

**Circular Pools**

Diameter x Diameter x Average Depth x 5.9 = Total gallons

For example: 18′ x 18′ x 4′ x 5.9 = 7,646 Gallons

**Oval Pools**

Length x Width x Average Depth x 5.9 = Total gallons

For example: 15′ x 30′ x 4′ x 5.9 = 10,620 Gallons

**How to determine the Average Depth of a Swimming Pool where the bottom slopes**

Below is a side-shot of the “typical” inground pool that has a shallow end (see “D”), then a slope that leads into the deep end (see “C”).

First measure the depth of “D”, the shallow end (usually anywhere from 3′ to 5′), and then measure the depth of “C”, the deep end (usually anywhere between 6′ and 12′). Then, add them together and divide them by 2. This is the average depth of your pool.

For example, if your shallow end “D” is 3′, and your deep end “C” is 8′, this would be your formula for the Average Depth:

3′ + 8′ = 11′

11′ divided by 2 = 5.5.

Therefore, in this example, your average depth would be 5 1/2 feet.

**Kidney and Irregular Shaped Swimming Pools**

There are two methods used to calculate the capacity of irregular shapes. First, you can imagine the pool as a combination of smaller, regular shapes. Measure these various areas and use the calculations described previously for each square or rectangular area and for each circular area. Add these volumes together to determine the total volume.

The total of measurement A plus measurement B multiplied by 0.45 multiplied by the length gives you the surface area of the kidney shape. (A + B = 18 feet). The rest of the calculations you are now familiar with. Try this volume calculation:

0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons)

0.45 x 18 ft x 25 ft x 5 ft x 7.5 = 7593.75 gallons.

**Rectangular In-Ground Pool Volumes in Gallons **

Pool Size(in feet) | 3.5 ftAvg Depth | 4 ftAvg Depth | 4.5 ftAvg Depth | 5 ftAvg Depth |

12×24 | 7,600 | 8,600 | 9,700 | 10,800 |

14×28 | 10,300 | 11,800 | 13,200 | 14,700 |

15×30 | 11,800 | 13,500 | 15,200 | 16,900 |

16×32 | 13,400 | 15,400 | 17,300 | 19,200 |

18×36 | 17,000 | 19,400 | 21,900 | 24,300 |

19×38 | 19,000 | 21,700 | 24,400 | 27,100 |

20×40 | 21,000 | 24,000 | 27,000 | 30,000 |

22×44 | 25,400 | 29,000 | 32,700 | 36,300 |

25×45 | 29,531 | 33,750 | 37,968 | 42,187 |

25×50 | 32,800 | 37,500 | 42,200 | 46,900 |

30×50 | 39,375 | 45,000 | 50,525 | 56,250 |

**All Answers Are In Gallons**

**Round And Oval Above Ground Pool Volumes In Gallons **

Size | 48in Wall* | 52in Wall* |

12ft Round | 2,975 | 3,398 |

15ft Round | 4,646 | 5,310 |

18ft Round | 7,646 | 8,602 |

21ft Round | 9,106 | 10,408 |

24ft Round | 11,895 | 13,594 |

27ft Round | 15,054 | 17,205 |

30ft Round | 18,585 | 21,240 |

33ft Round | 22,488 | 25,700 |

12x24ft Oval | 5,948 | 6,797 |

15x30ft Oval | 9,293 | 10,620 |

16x32ft Oval | 10,573 | 12,084 |

18x33ft Oval | 12,267 | 14,019 |

**Assuming water depth is 6 inches less than wall height.**

All Answers Are In Gallons

All Answers Are In Gallons