The weight percent of sodium hypochlorite is the weight of the sodium hypochlorite per 100 parts of solution.  It can be calculated by converting the weight percent of available chlorine into its equivalent as sodium hypochlorite by multiplying the ratio of their respective molecular weights:

Note:  When measuring the specific gravity, measure it at the same temperature as the temperature of the bleach sample used in the bleach strength test.

Weight percent available chlorine x NaOCL/Cl2 or x 74/71 or 1.05 weight percent NaOCl

Weight percent sodium hypochlorite

= (gpl available chlorine x 1.05)/(10 x specific gravity)

or = (trade % Available Cl2 x 1.05)/specific gravity

or = weight percent available chlorine x 1.05

Since sodium hypochlorite is sold based on the strength of the product, it is critical to specify exactly which term is used to define the strength of the product.