Dividing the trade percent by the specific gravity of the solution gives weight percent of available chlorine. 

Typically, density measurements will result in errors of 0.5 to 1.0% (i.e. 10% could be 9.90% to 10.10%) when converting from gpl available chlorine to weight percent available chlorine.

Weight % Available Chlorine = gpl available chlorine /(10 x specific gravity)

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.