The specific gravity of the sodium hypochlorite solution is the ratio of the weight of the solution with respect to water. If the product has a specific gravity of 1.2, a gallon of this sodium hypochlorite weighs 10.00 pounds (1.2 * weight of water). The specific gravity of sodium hypochlorite with the same strength may vary due to the amount of excess caustic in the solution.

Most tables that show the gpl of available chlorine and the specific gravity of the solution were created 40-50 years ago. These levels are shown with excess sodium hydroxide (caustic) being much higher than the levels of sodium hydroxide typically produced by current manufacturers. The reason excess caustic levels have decreased is due to the improvement in manufacturing techniques. In addition, the endpoint control of the chlorine and caustic reaction is better.

The old tables will typically show 120 gpl available chlorine with 0.73 % by weight excess caustic which
results in a specific gravity of 1.168 at 20 degrees C. If the excess caustic is removed, the specific gravity will be approximately 1.157.

Typically, the sodium hypochlorite produced by a continuous process will have approximately 0.2% by weight excess sodium hydroxide and this would result in a specific gravity of 1.160 at 120 gpl. These numbers assume the salt is in solution with the bleach and very small levels of chlorate exist in the solution.