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Pool Volume Calculator: How Many Gallons Of Water Are In Your Pool?

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

There are often questions that people ask that seemingly many others believe to be futile. Someone asks “how much water is in your pool in gallons?” and you may think, “well – who cares?” 

The fact is though, knowing how much water is in your pool is not only good knowledge (because, why not?!) but also good to know because it will factor into the amount of chemicals you put into the pool.

How Many Gallons Of Water Are In Your Pool?

Accuracy for this is important because it may mean the difference of how long your pool survives over time, along with the safety for everyone involved.

Therefore, it’s critical that we know how to work out how much water you have in your pool. We’ve got a handy guide below which details all of this for you and includes what else you may need to know about your pool. 

How To Calculate The Amount Of Water In Your Pool: The Start

Before we get started, there are some things you should know before calculating the amount of water in your pool. This information can help you understand how to calculate the amount of water in a pool and make sure you’re getting accurate results.

You need to know the metrics to use before you begin. You’ll need to know: 

  • Length
  • Width 
  • Diameter
  • Depth 
  • Radius 
  • Pi

The overall surface area is calculated by multiplying the length by the width of your pool. However, to determine the answer – we must first understand that not all pools are the same shape. So, let’s look at different pool shapes to understand how to proceed. 

Round Pool 

You need to start with determining the diameter of your pool. Once you’ve got the diameter, you can divide that by 2 which gives you the radius. With the radius and the depth figures, you can present yourself with the following formula:

Pi x radius x depth x 7.5 = volume in gallons. 

Rectangular Pool

To determine the volume of water in gallons within a rectangular pool is pretty simple too, but the calculations may need adjusting slightly depending on the slope of your specific pool. 

Let’s say you have a constant, flat surface depth on the bottom of your pool. You will work out the surface by multiplying the length of the pool by the width of the pool – and then multiply that answer by 7.5. 

So, you have: 

Length x width x 7.5 = volume in gallons. 

If however, your pool has a shallow end and a deep end, you’ll need to account for this. To do this and get an accurate answer, you’ll need to calculate the depth of the shallow end and add this to the depth of the deep end and divide this by 2. 

This will give you an average overall pool depth. So, you’d have:

Shallow depth + deep depth divided by 2 = average depth 

Length x width x average depth x 7.5 = volume in gallons. 

Custom Pools 

If you have a custom, free-formed pool – whilst they are nice to look at, they’re incredibly difficult to calculate the volume in gallons. 

The best thing you can do is to do everything in small amounts. Effectively you make the pool into small, manageable dimensions and determine the volume overall, using the above formula. 

Do I Need To Know The Water Volume Of My Pool?

It’s always good to be aware of the volume of water in your pool, so you can ensure it doesn’t overflow or flood.

It’s also important to know if your pool needs servicing. A lot of people think their pool is fine until they notice leaks or other issues. By knowing the volume of your pool you’ll be able to see whether your pool needs maintenance.

How Do I Measure The Water Level In My Pool?

There are many ways to measure the level of water in your pool, but the easiest way is to use a float. Floats are available from most hardware stores and come in various sizes. They are cheap and easy to use. 

They simply sit on top of the water and as the water rises up, it pulls the float down. If the water is low enough, the float won’t move. As the water rises higher, the float moves further away from the wall and eventually sinks below the water line.

This is when you know the water level is high enough. 

Do Chemicals Make A Difference To The Volume?

Chemicals like chlorine and bromine can affect the volume of water in a pool but the formulae for calculating the volume remains the same. 

The Bottom Line

Knowing how much water there is in your pool is essential. It helps you keep track of the amount used and ensures you don’t run out of water. Knowing the volume of your pool also means you can plan ahead and add more water if needed.

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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