Chlorine Dose Calculator: Product Amount & FC Change

Chlorine dosing is a mass balance. A "ppm" is one milligram per liter, so to raise free chlorine by a given amount you need volume × ppm change × product strength worth of product. The calculator works in liters internally, then converts to the fluid ounces, ounces, or pounds you actually measure out.

The only variable between products is the **available chlorine** percentage — the fraction of the product's weight that acts as chlorine. Liquid chlorine (sodium hypochlorite) is 12.5%, cal-hypo is 65% or 73%, dichlor is 56%, and trichlor is 90%. A stronger product means less of it for the same result, which is why one gallon of 12.5% liquid raises 10,000 gal by about 15 ppm while it takes roughly two pounds of 65% cal-hypo to do the same.

Always add the product to a bucket of water or broadcast it across the deep end with the pump running — never pour water onto concentrated chemical. Test with a kit first, dose, then retest before adding any more. Dichlor and trichlor also raise cyanuric acid, so use them sparingly if your stabilizer is already high.