Hot Tub Supply Spa Depot
Water Volume
How to figure it out.
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Hose end spa filling filter

It's helpful to know your spa's water capacity to determine chemical dosages.  Textbook formulas for calculating volumes of geometric shapes do not work well for spas which have internal features such as seats and contours which displace water. We've developed two methods to give you fairly accurate estimated hot tub water volumes.

Method #1: Fill Time

The most accurate way to determine the volume of a spa, without fancy equipment, is by fill time.  First, using a stopwatch or wristwatch time how long it takes to fill your spa.  Convert minutes and seconds to total seconds, and write it down. Then while the water is still running (using the same hose and pressure) time how many seconds it takes to fill a 1-gallon bucket.

Now divide the number of seconds it took to fill your spa, by the number of seconds it took to fill the gallon container, and you will have the approximate water volume!

Example:  You filled your spa in 30 minutes (1800 seconds) and filled the one gallon container in 6 seconds.  1800 divided by 6 = 300 gallons.

Spa water volume by fill-time Using a five gallon bucket will result in an even smaller margin of error.  Using the above example with a five gallon bucket:  You filled your spa in 1800 seconds, and filled the five gallon bucket in 30 seconds.  1800 divided by 30 = 60 five gallon buckets, or 300 gallons.

Method #2: Outside Dimensional

The dimensional method is not as accurate as the fill-time method, but is a quicker way to determine the approximate volume of any spa. Our formulas were developed using data from industry averages, and make estimation easy because they allow you use the outside dimensions of a portable spa cabinet. (Using inside dimensions is nearly impossible with all of the odd shapes and interior features of a portable spa).

Spa outside dimensions

Type of Hot Tub   Formula (take all measurements in inches)

Square or rectangular portable spas with seating.   Spa water volume formula
Round or multi-sided portable spas with seating.   Spa water volume formula
Square or rectangular spas without seating, inground spas.   Spa water volume formula
Round, irregular shaped, wooden, multisided soft spas, etc.   Spa water volume formula



Results are estimated volume only.  Consult with manufacturer.





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