Last Updated: June 27, 2022

Pool Volume Calculator

Written By: Pool Care Guide

Your pool volume is the cornerstone metric for your pool care because everything is measured by how many gallons are in your pool.

In all of these cases, you are ultimately trying to measure and multiply the length, width, and depth to find the cubic footage of the pool.  When you have the answer you can multiply it by the amount of water that fits into one cubic foot of space (7.48 gallons).

There are three primary ingredients to calculate the volume. You need the length, width, and depth. For many pools, it’s a straightforward process. Those cubed designs aren’t exactly challenging to measure. This process becomes just a bit more complicated when you have a pool with irregular shapes and changing depths. However, before we get to that, we'll need to know some definitions.

Definitions to Know When Calculating Pool Volume

In this guide, we use a few basic mathematical terms. To defend against the perils of monotony, we have listed their definitions here. If there is a word you don’t know, just pop up here to get the explanation.

Diameter: Draw an imaginary line across the center of a circle. The length of that line is the diameter of the circle.

Radius: The radius is exactly half the length of the diameter. Measure across and divide by two. 

Square: When you multiply a number by itself, you are squaring that number.

Area: (Length x Width) The area is a measurement of 2-dimensional space. You can use this to find the dimensions of a flat surface such as a wall, floor, or pool.

Volume: (Length x Width x Height) Volume is a measurement of 3-dimensional space. You can calculate it by density, weight, or displacement. If you know the square footage of a space, and you know how many grams per centimeter can fit into it, you can calculate 

How Much Water Can Fit Inside One Cubic Foot?

If we measure the cubic footage of the pool and we know how many gallons fit in a cubic foot of space, we can calculate how much water is in the pool.

Every cubic foot in your pool can hold 7.48 gallons of water. Let’s see an example of how you will use this. If your pool has a volume of 4,000 cubic feet, this is water the calculation would look like

Where Should You Calculate the Depth?

Depth is one of the measurements that you are going to need to make. When you measure it, do not measure from the bottom of the pool to the top. A pool’s water level should reach the middle of the skimmer; no higher, no lower. With that in mind, you should measure from the pool’s floor to the middle of the skimmer.

How to Measure Irregularly-Shaped Pools

Not every pool has a simple box shape with an unchanging 5ft depth. Those simple designs are straightforward, easy to measure, and the pool volume is simple to calculate. 

Many pools are asymmetrical, built with variable depths and complex shapes. An irregularly shaped pool becomes easier to measure if you stop looking at it as one pool. Notice the shapes and transitions. It’s often easier to measure and calculate their volumes separately. After that, you can add them all together to calculate the pool’s total volume in gallons. 

Unless you drain the pool and account for fine details, measurements are unlikely to be exact. However, unless the estimates are exceedingly rough, they will almost always be close enough for doses of pool chemicals and purchasing pool equipment. 

How to Calculate Variable Depth?

Pools with changing depths are common, and the difference in volume is still easy to calculate. The way we calculate these changes will depend upon the way the floor transitions.

Gradual Slope

If a pool’s depth transitions gradually from one end to the other, this calculation becomes easy. We just need to average the shallowest depth and the deepest depth. You can find the average by adding these two depths together and dividing by 2.

Drop-off Depth Change

Some pools don’t smoothly transition from one depth to another. Instead, some suddenly switch from the shallow end to the deep end and vice versa. If these sections each take up 50% of the pool, treat them the same as a sloped floor (i.e., Add both depths and divide by 2).

If each depth has a different surface area, separate the pool into sections. Treat the deep end as one pool and calculate its volume. Then do the same with the shallow end. The specific formula(s) that you will apply will depend upon the shapes of each section of the pool. 

Pool Shapes and Their Volumetric Formulas

The Basic Shapes

Pools come in all shapes, sizes, and slants, so calculating the cubic feet can differentiate a little bit from pool to pool. If your pool’s design is particularly crazy, don’t worry. When you know the basics, even complicated pools can be simple to measure.

For the sake of clarity, we will add the formulas used, show example problems, list out the steps, and even the logic behind them if we believe it is useful. If you understand the equations and follow them in the order listed, reading the steps will be unnecessary.

Finally, if your pool has varying depths, the average depth should be used in the equations further down this page. The instructions for average depth are listed higher on this page under the section, “How to Calculate Variable Depth.”

Step 1: Measure the Length, Width, and Depth

We need three measurements to calculate the area and volume of our pool and how many gallons it can hold. The length and width are obvious. 

The depth can potentially be a tiny bit trickier. First, be sure not to measure from the top of the pool. Measure from the midpoint of the skimmer to the floor of the pool.

Write those measurements down and move on to the next step.

Step 2: Calculate the Area

We can calculate the area of the pool’s flat surface by multiplying the length by the width. In our example, you will see that our width is 10 feet and our length is 40. That makes our example equation come to a total of 400 square feet.

Step 3: Calculate the Volume

To calculate the volume of our pool, we need to multiply the square footage of its surface area by its depth. 

In our example, you will find that we used a depth of 5 feet. Multiplying 5 feet by the surface area’s 400 square feet brings us to a total volume of 2,000 square feet.

Step 4: Calculate the Total Gallon Capacity

7.48 gallons of water fit into a single cubic foot of space. If we multiply 7.48 gallons with the square footage of our volume, we will know our pool’s total gallon capacity.

In our example, we will multiply our 2,000 square feet of volume against 7.48. The product of these numbers shows us that our pool can hold 14,960 gallons of water.

Step 1: Measure the Radius

To find the radius, measure across the center of the circle and divide that number by two.

Step 2: Calculate the Area

A circle's area is the combination of its length and width. However, due to its troublesome shape, we need to calculate that surface area a bit differently.

To find the length and width, we need to rearrange the circle. Picture a pepperoni pizza. If you take those slices and arrange them like this, “▲▼▲▼▲” you will create a parallelogram. Parallelograms can be calculated like a regular square. 

When rearranged in this new shape, the radius = height, and the width = radius x 3.14. That’s why we get the equation of a circle’s area is equal to 3.14 x Radius². Essentially, this equation is saying (Radius x 3.14) x (Radius)=Area of Circle

In our example, Radius = 3.82 feet. If we square this number 3.82 x 3.82=14.59 and times it by pi (3.14), we will get a surface area of 45.82 square feet.

Step 3: Calculate the Volume

We don’t live in a flat world, so we need to add some depth to this 2-dimensional circle. In our pool example, we’ve measured the depth to be 5 feet. If we multiply the depth by our area of 45.82 x 5 = 229.1 square feet, it will stretch the area of our flat circle into the 3-dimensional world. That gives us our volume, Volume = 229.1 Square Feet

Step 4: Calculate Total Water Capacity

As we already know, 7.48 gallons can fit into one cubic foot of space. If we multiply that against how much cubic space we have in the pool (229.1 x 7.48 = 1,714 gallons), we will have our pool’s volume.

Step 1: Measure the Major and Minor Axis

The minor axis and major axis are respectively referring to the oval’s shortest and longest diameters. In the above example, our major axis is 24 and our minor axis is 15. Half of a diameter is its radius. To show this,  so that’s why we stuck the axes atop the 2 denominators in the example above this paragraph.

Go to your pool and stretch a measuring tape over the widest and narrowest parts of the oval. Write those two numbers down for the next step. 

Step 2: Calculate the Area

An oval is to a circle, as a rectangle is to a square. When you measure the area of an oval, you are performing the very same formula as the circle’s Circle Area = 3.14 radius². We only need to account for the oval’s irregular shape.

Radius²is the same as saying radius times radius. For the oval, we use the radius at the narrowest point and the radius of the longest point. We call the shortest diameter the minor axis, and we call the longest diameter the major axis.

In our example, we measured our minor axis to be 15 feet wide and the major axis to be 24. We divide each of those by 2 to get the radii which will make our equation look like

Step 3: Calculate the Volume

Add a little depth. Measure from the floor to the midpoint of the skimmer door. Now multiply that measurement by the square footage of the area. For our example, that is our area of 282.6 square feet against our 5 feet of depth. 282.6 x 5 = 1,413 square feet

Step 4: Total Gallon Capacity

As we learned earlier, 7.48 gallons of water fit into one square foot of space. If we multiply our pool’s measured square footage against 7.48, it will give us its total gallon capacity. Continuing with our example, the equation presents as 1,413 x 7.48 = 10,569 Gallons.

Step 1: Gather the Measurements

Kidney pool shapes are formed by two rough circles connected by a slightly pinched center. To begin our calculations, we need the diameters of each circle. Measure through their centers, across the widest points, without penetrating the circumference of the circles. 

Now measure the length of the pool at its longest point.

Step 2: Calculate the Area

Adding the diameters of each circle and multiplying them by .45 averages out the circles and mathematically reshapes the kidney into a rectangle. Another way of seeing it is that the product of .45 x (Diameter Circle 1 + Diameter Circle 2) gives us our width. 

When we multiply .45 x (Diameter Circle 1 + Diameter Circle 2) against our length, we are solving the familiar equation Area = Length Width. In our example, we plugged “10” for diameter 1, “15” for diameter 2, and “20” for the length of the pool. 

In our example above, we plugged “10” for diameter 1, “15” for diameter 2, and “20” for the length of the pool. 

Step 3: Calculate the Volume

Once you have the area, the volume becomes super easy to calculate. Just multiply the depth by the area’s square feet, and you will have the pool’s volume. For our example, we used a depth of 5 feet.

Step 4: Calculate Total Gallon Capacity

It’s the last step. We know our pool has a volume of 1,125 square feet of space, and we know that 7.48 gallons can fit into each one of them. With that, we can calculate the pool’s total gallon capacity by multiplying them together.

Okay, that’s all we have for now. Please let us know if you have any suggestions or requests regarding this guide.

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