In order to figure out the proper doses of chemicals for your pool, you need to determine how many gallons of water it holds. To do that, you need to use a ruler to measure your pool to find out these four different numbers; Length, Width, Average depth and a multiplier that determines gallons.
So here are the formulas to figure out how much water is in your swimming pool:
These formulas hold true for both In-ground pools 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
Diameter x Diameter x Average Depth x 5.9 = Total gallons
For example: 18′ x 18′ x 4′ x 5.9 = 7,646 Gallons
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 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 or hot tub 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 capacity.
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
Round And Oval Above Ground Pool Volumes In Gallons
|Size||48in Wall*||52in Wall*|
All Answers Are In Gallons
What Is Parts Per Million (ppm)
One of the most important calculation you will use is parts per million (ppm). The amount of solids and liquids in the water is measured in parts per million, as in three parts of chlorine in every one million parts of water, or 3 ppm.
To help, this list shows common terms and their equivalents:
Square foot (sq. ft.) = 12 inch wide x 12 inch long
Cubic foot (cu. ft.) = 12 inch wide x 12 inch long x 12 inch high
Cubic yard (cu. yd.) = 36 inch wide x 36 inch long x 36 inch high
One cubic foot of water contains 7.48 gallons
One cubic foot of water weighs 62.4 pounds
One gallon of water weighs 8.33 pounds
One part per million (ppm) represents 8.3 pounds of chemical per million gallons of water.
However, one gallon of chlorine, for example, poured into one million gallons of water does not equal 1 ppm. That is because the two liquids are not of equal density. This becomes obvious since a gallon of water weighs 8.3 pounds but a gallon of chlorine weighs 10 pounds (in a 15 percent solution). The chlorine is a denser liquid; there’s more of it than an equal volume of water.