how to measure a swimming pool for water volume calculation

Welcome to our swimming pool math section – swimming pool volume calculations. Find the pool water calculator you are looking for below including: pool water chemistry conversions! (Some features are coming soon)

Note: This is used for spas that are round and does not subtract for the benches inside of the spa. Irregular shape pool volume calculator is coming soon. 

Having concerns about these results? > Ask a pool pro!


Swimming Pool volume calculation:
Volume is the amount of space taken up by a three-dimensional object, like a swimming pool. Volume often refers to liquid volume, which is the amount of space taken up by a liquid that completely spreads to fill its container. This is an approximate calculation of the total amount of gallons the pool can hold, also known as pool capacity. You will need to know how many gallons of water your pool holds to properly administer the chemicals and / or when you need to make special adjustments to the water when you experience an adverse pool water condition.


If the reasons are not obvious, here is why. You will need to know a few approximately accurate details regarding your pool specifically. The reasons are for pool water treatment using chemicals. Without knowing how much water your pool holds you will not know how to determine the amount of chemicals to add to the pool. 

Note: If you are the original owner of the pool you should have documents and drawings that include the pool measurements, in this case you can skip the measuring procedures, you should have what you need already.

How to use our pool math calculators:

You should have notes on your swimming pool, namely the size and depth information at the least. If you do not already have notes saved about your pool, go and create a notebook dedicated to the pool, it will come in handy more times than you think.

Now that you have a means of keeping notes on your pool, let’s begin with “How to measure your pool for water calculations”.

Here are the tools you will need to get all the measurements:

  • A tape measure (that is at least 30ft long)
  • The pool pole
  • You might need a second person to help hold your tape measure

Now that we have the tools needed to measure the pool, let’s actually get those measurements, here is how you do it.


Rectangle pool shape measurements:
: Areas of the pool that are cut out from the main shape will need to be added in to the measurements. This can also be used for measuring square & rectangle spas.

  • Step 1 – Measure the total length of the pool from the inside wall to the adjacent inside wall. (from tile tot tile on opposite sides)
  • Step 2 – Measure the total width of the pool inside wall to inside wall.
  • Step 3 – Measure the depths. Get your pool pole and lay it across the deep end width to width approximately directly above the deepest point. Use your tape measure from the bottom of the pool up to the pool pole and subtract 3 inches. Repeat this again for the shallow end.
  • Step 4 – Record all of these measurements into your notes about the pool.
  • Step 5 – Use our pool volume calculators above with the numbers you have to get the total water volume capacity of your pool.

Circular pool & spa shape measurements:

  • Step 1 – Measure the total diameter of the spa and divide by 2 to get the radius.
  • Step 2 – Measure the depth by using the tape measure at the center of the spa bottom up to the water level. Typical spa depth is around 42 inches of water.
  • Step 3 – Record these numbers in the spa section of your notes.
  • Step 4 – Use our circular volume calculator above to get the approximate water capacity of the hot tub or spa.

Ellipse, Oval, and Irregular shape pool measurements:

Interesting finds when measuring pools:
Often times we see that pool owners are surprised when they realize the pool is either less or more deep than what they were told. This is evident when accurately measuring the pool to double check what you were told by the pool builder or the home seller. Many people do not know they were shorted a few inches to nearly a foot of pool depth until they actually put a tape measure to it in the right way. Unfortunately many pool builders will try to skimp on small things like this in an attempt to save themselves a little money on materials.