Using Chlorine Addition to Figure out Pool Volume


Apr 12, 2017
Grapevine, TX
I am trying to get a better handle on my pool volume. The overall shape is kidney and the depth varies from 3 ft. to 9 ft. The slope is not gradual so it is more deep than shallow. I also have steps, built in stools, and some type of shelf built in. I've used the method to measure kidney shaped pools and came out with about 21,500 gallons. Last night I measured my FC and came out with 5 ppm. Plugging the 21,500 gallon figure into pool math I needed to add 159 oz. of 8.25% bleach to bring me up to my target FC of 10 ppm. I added exactly the amount of bleach I needed and waited an hour to re-test. The re-test showed I raised my FC to 9 ppm. Playing around with pool math, I changed the target FC to 9 and kept upping the gallons until I hit the 159 oz. of recommended bleach again. This had me at 26,800 gallons.

Is this a valid method of figuring out my pool volume? Are there too many variables, such as actual bleach strength, to accurately rely on the new 26,800 gallon number?


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

It's kind of like Hand Grenades... Close is close enough... :p

What you suggest will give you a close enough estimate to your pool size.

I would not go by just one test, but over time you should be able to get a pretty accurate reading.

Nothing we do here needs to be that precise..


Jim R.


TFP Expert
Platinum Supporter
May 23, 2015
Tucson, AZ
If you want to waste a lot of TA reagent, you can do this - A Chemical Way of Calculating Pool Volume

It's more accurate than using other forms of chemical additions but it uses up a lot of TA reagent. It will get you to within 1000 gallons or so of the actual volume. I did try it once and it works, but you will use A LOT of R-0009 and R-0008....


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
You almost have it. There's too many variables for that to work. The tolerance on the FAS-DPD test. Bleach strength. Water volume varies day-to-day from evaporation. Could be some organics in the skimmer or pump basket robbing FC.

My pool was estimated to be 15000 gallons. I kept coming up short when I'd add acid to lower pH and when I added bleach. Consistently. My TA drop --- and it was real high at one time, so each acid addition made a measurable drop in TA -- was never what Effects of Adding Chemicals said it should be. So what I did was add 500 to the pool volume in poolmath and monitored results for a couple weeks. Still not reaching the predicted change. Another 500 gallon. Boom. Right on the nose.

Other Threads of Interest