Here is the formula I use for manually calculating chlorine. 1,000,000/10,000 x .95 x 0.0825 = 7.8

One million divided by the total gallons of water in pool, then multiplied by .95 (121 oz of chlorine is converted to a decimal) x 0.0825 (% of chlorine in jug).

121 oz is the amount of bleach in the jugs of bleach I use.

Hope this helps you.