Weight to Volume Conversion - Borax


Active member
Aug 20, 2019
Hamilton, MI
Anyone know with any certainty what the approximate weight to volume conversion is for Borax?

My PH has always been very steady, but recently has been dropping slowly... presumably due to limited use (new boat), and thus little aeration... so I plan to adjust with Borax to get it back into the sweet spot. BUT, I don't have a reliable scale handy, and pool math is providing additions of Borax by weight. The interwebs have lead me to differing conversaions ranging anywhere from 0.9 to 1.8... with one site saying that "1 dry ounce by volume equals 1.8 oz by weight"... and another saying that "1 cup of borax by volume (8 oz) weighs just 7.2 ounces"....

Either way, I plan to start small and add a little as I go over a couple days, while recording my additions, but it would be nice to know when I add 5 ounces by volume what I'm truly adding in comparison to what the poolmath app is recommending.


Gold Supporter
Bronze Supporter
Jun 11, 2018
Verona, MO
Strange, I didn't think PH would lower without adding something. What is your PH now? Still within range...>7.2?
What is your TA?


TFP Expert
Mar 2, 2011
1 oz weight = about 1 oz dry volume.