Knowing how many gallons of water are in your pool is important for determining things like the parts per million (PPM), the right amount of chemicals to add, heater size, and much more. But how do you get started calculating the capacity of your swimming pool? Use my pool volume calculator below to get started.
Pool Volume Calculation Basics
You need a few basic metrics to calculate the volume of your pool.
- Pi (3.14 constant)
Multiplying the length and width of your pool gives you the surface area it occupies. Throw depth into the equation, and you start getting to basic volume calculations. Make sense? Okay, let’s jump into more specifics for different pool shapes.
Rectangular Pool Volume
Determining the volume of a rectangular pool is pretty straightforward, but your calculation will vary slightly depending on the slope of the bottom of your pool.
If your pool has a constant depth across the bottom, you’ll determine the pool’s surface area (length x width), multiply that by the depth of the pool, and then multiply by 7.5 to calculate the volume in gallons.
Length x width x depth x 7.5 = volume (gallons)
Volume of Pools with Variable Depth
Many pools aren’t that simple – you have a shallow end and a deep end. To determine the volume of a pool with variable depths, you need to calculate the average depth of the pool. Do this by adding the shallow end to the deep end and dividing by 2.
(shallow depth + deep depth) / 2 = average depth
From there, the equation is similar to our constant depth example.
Length x width x average depth x 7.5 = volume (gallons)
Alright, let’s move on to round pools.
Round Pool Volume
For round pools, you need to start by getting the total diameter of the pool. Divide that diameter by 2 to get the radius of the pool. After you get the radius and depth, plug those into the formula below.
3.14 × radius2 × depth × 7.5 = volume (gallons)
Pretty simple! However, not all pools are simple rectangles and circles.
Kidney or Irregular Shape Pool Volume
Calculating the volume of a standard rectangular or circular pool is relatively easy, but when the pool is irregularly shaped, things get a bit more complicated. Irregularly shaped or kidney pools are super popular and a lot of fun from a design perspective, but they are a bit of a headache to calculate the volume of. But don’t worry, it is still totally possible. You’ll just need to do a bit more math! In this section, I’ll go over my top methods for calculating the volume of irregular pools.
Break It Into Small Sections
Rather than attempt to calculate the volume all in one go for a kidney or irregular pool, you’ll want to break it up into bite-sized chunks. For a kidney pool, you can essentially cut the pool in half and calculate the volume of each half. If your pool has 3 or more sections, measure and calculate the volume of each section and then add them together.
Calculate the Volume
You can also calculate the volume of your kidney-shaped pool using this simple equation:
A is the widest point of your pool
B is the second widest point of your pool
0.45 x (A+B) x total length x average depth x 7.5 = volume
Using this equation, you’ll be able to calculate the approximate volume of an irregular kidney pool.
Calculating Parts Per Million (PPM)
Parts per million is a calculation you’ll become very familiar with as a pool owner. One part per million means there is 1 pound of a chemical for every million pounds of water. Keep in mind that one million pounds of water = 120,000 gallons. So, when calculating how much of a certain chemical you must add to your pool, you should first calculate the volume of your pool and then work out how many pounds of the chemical to add to your pool.
If you need to add 1 PPM, you should add 1 pound of chemical for every 120,000 gallons of water. This means if your pool is 60,000 gallons, you’ll add half a pound, and if it is 30,000 gallons, you’ll add a quarter pound.
Need to Call a Professional?
Tired of all the math? Call a professional pool builder in your area, and they can do all the work for you to determine things like pool size, depth, heater size, and a bunch more. I can help you find a good contractor if you need help; just shoot me a message. I also recommend reading these articles below if you’re just getting started with managing your swimming pool. Best of luck!