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How Many Gallons Of Water Are In My Swimming Pool Or Spa?

How many gallons of water do I have in my pool or spa?

 Knowing how many gallons of water you have in your pool and spa is one of the foundational pieces of the puzzle in running your aquatic facility or backyard pool in a safe and healthy way. Even though knowing your pool and spa volumes crucial, it is truly an often overlooked component of operating your pool. Knowing pool and spa volume is crucial for the following reasons:

  • Accurate Chemical Adjustments
  • Bather Load
  • Circulation Needs

How do I add chemicals to my pool correctly?

 Without knowing exactly how many gallons of water are in a pool or spa, it is impossible to properly add chemicals or make crucial adjustments. All chemical manufacturers ship their chemicals with dosage instructions, or those instructions are printed on the chemical’s label. These dosage instructions will call for a certain amount of their product per 10,000 (or at times 7,500 or 5,000) gallons. If you don’t know how many gallons are in the pool or spa, it is a guessing game as to how much chemical to actually add at that point! 

This lack of precision oftentimes leads to overdosing or under-dosing, neither of which are safe or recommended. Overdosing can mean harmful reactions amongst swimmers and damaged equipment that will need to be replaced more often than necessary. Under-dosing means the potential transmission and spread of harmful pathogens to swimmers and could also result in equipment failure. 

We want to prevent any of these scenarios from occurring in our pools or spas, and calculating the volume correctly is the first step in preventing issues. The formula used for rectangular pools is: 


Length x Width x Average Depth x 7.5


The formula used for circular spas is:


Radius x Radius x 3.14 x depth x 7.5


It is also crucial for you to remember that spas have two areas, the seating area and the footwell area, so each area needs to be measured independently. Those two volumes are added together to determine your total spa volume. 


How many people are allowed in my pool or spa?

Our pools and spas are resilient in spite of the beating they can take from swimmers. But over time our pools begin to show fatigue through cloudy water, early algae growth, and other unsightly issues. It is crucial to understand how many swimmers your pool or spa can handle before it starts to show signs of fatigue.  As an operator it is important to remember that 1 swimming will neutralize the disinfectant in roughly 600 gallons of water. Equipped with this knowledge, we can use the result of our volume calculation to determine how many swimmers our pool or spa can handle safely. The bather load formula is as follows:


Pool Volume ÷ 600 = Bather Load


For example, if I have a 68,000 gallon pool I can take that number divided by 600 to determine my bather load. That means I can get 113 people through my pool in a 6-hour (1turnover) time period before my pool is going to start looking cloudy and overwhelmed. 

 NOTE: Bather load is different than capacity. We will cover capacity in another post. 


How do I figure out what my flow rate needs to be in my pool or spa?

Pool and spa volume is also required to figure out what our flow rate needs to be. If you are curious what flow rate is, please click here to find out more about flow rates. Our minimum flow rate can be determined by taking our pool volume divided by the turnover rate required by your local health department (usually 6-hours for commercial facilities) and then divide by 60 minutes. The formula looks like this: 


 Volume ÷ Turnover Requirement ÷ 60 = Minimum flow rate 



How do I become a CPO (Certified Pool Operator)?

 As we have just seen in this piece, operating a pool and spa can be very challenging and complicated. That is why Pool Training Academy offers Certified Pool Operator (CPO) Courses that cover the topic of volume and so much more. Our multi-award winning instructors have taken their decades of hands-on pool and spa experience and combined it with the high-quality instructional materials and research from the NSPF (National Swimming Pool Foundation) to provide hands-down the best Certified Pool Operator experience around. Our course locations vary from the front range of Denver, Colorado to Kansas City, Missouri, Missoula, Montana to Albuquerque, New Mexico and beyond. Click here to find a course near you and become a pool and spa expert with Pool Training Academy’s Certified Pool Operator Courses. 

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