What is the percentage of chlorine residual in typical household bleach?

• A. 3%
• B. 7%
• C. 10%
• D. 5.25%

Answer: (D)

Household bleach is a solution of sodium hypochlorite, and the strength you’ll typically see labeled is about 5.25% available chlorine. This is the standard concentration used for disinfection in many guidelines, so it’s the best match for what “chlorine residual” in typical household bleach refers to. The other percentages are not the common label strengths of ordinary household products. Understanding this starting concentration lets you calculate proper dilutions for disinfection (for example, diluting 5.25% bleach to a much lower final concentration, such as roughly 0.1%, by using about a 1:50 dilution), which is why the 5.25% figure is the correct reference.