How To Calculate How Much Water Is In Your Pool

Knowing the capacity of your pool is the key to correctly treating the water with chemicals, to know the correct size of the pump you have to use and to choose the filters, among other things. To calculate the volume of your pool in gallons, you just have to apply a very simple formula that will depend on its shape. Follow these steps if you want to know how to do it.

Equipment you will need

  • measuring tape
  • calculator
  • pen and paper
  • someone to help you

How To Measure The Length And Width Of The Pool 

If it’s rectangular, measure only one of the two long sides and one of the two short sides. If it is square, measure only one side, since in a square all four sides are the same length. If your pool is round, measure only the diameter, which is a straight line that passes through the center and cuts the circumference at two points.

How To Measure The Depth Of The Pool

This is the other fundamental dimension to know the volume of a pool. If yours has a homogeneous depth (like most pools that are above ground level), you just have to measure the distance between the bottom and the edge (height). But if, as in most pools, in yours the depth gradually increases, you will have to measure the minimum depth (where the water level is lowest for the swimmer) and the maximum depth (where the water level is higher for the swimmer).

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 Calculate The Depth Of A 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”).

How many gallons of water are in my pool?

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 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 ft
Avg Depth
4 ft
Avg Depth
4.5 ft
Avg Depth
5 ft
Avg Depth
12×247,6008,6009,70010,800
14×2810,30011,80013,20014,700
15×3011,80013,50015,20016,900
16×3213,40015,40017,30019,200
18×3617,00019,40021,90024,300
19×3819,00021,70024,40027,100
20×4021,00024,00027,00030,000
22×4425,40029,00032,70036,300
25×4529,53133,75037,96842,187
25×5032,80037,50042,20046,900
30×5039,37545,00050,52556,250
All Answers Are In Gallons

Round And Oval Above Ground Pool Volumes In Gallons

Size48in Wall*52in Wall*
12ft Round2,975 3,398
15ft Round4,646 5,310
18ft Round7,646 8,602
21ft Round9,106 10,408
24ft Round11,895 13,594
27ft Round15,054 17,205
30ft Round18,585 21,240
33ft Round22,488 25,700
12x24ft Oval5,948 6,797
15x30ft Oval9,293 10,620
16x32ft Oval10,573 12,084
18x33ft Oval12,267 14,019
Assuming water depth is 6 inches less than wall height.
All Answers Are In Gallons