Calculate how much bleach and water to mix to reach a target disinfecting concentration in percent or ppm based on your stock bleach strength.
Bleach Dilution Formula
To find how much concentrated bleach you need to reach a target concentration, the dilution equation is rearranged for the stock volume:
V_1 = (C_2 \times V_2) / C_1
The water you add is the remaining volume:
V_{water} = V_2 - V_1
To find the concentration of a mix you already made:
C_2 = (C_1 \times V_1) / V_2
Where C_1 is the stock bleach concentration (the percent sodium hypochlorite printed on the bottle), V_1 is the volume of stock bleach used, C_2 is the target or final concentration, V_2 is the total final volume of the mixed solution, and V_water is the volume of water added. Concentration can be entered in percent or in parts per million, where 1 percent equals 10,000 ppm.
Bleach Strengths and Disinfection Targets
Use these typical values to fill in the stock concentration and to pick a target concentration for your task. Always check the label, since chlorine strength varies by product and weakens with age.
| Product | Typical Sodium Hypochlorite |
|---|---|
| Regular household bleach | 5 to 6 percent |
| Concentrated household bleach | 7.5 to 8.25 percent |
| Industrial or pool grade | 10 to 12.5 percent |
| Use | Target Concentration |
|---|---|
| Sanitizing food-contact surfaces | about 200 ppm |
| General hard-surface disinfecting | about 600 to 1,000 ppm |
| Heavy disinfection of bodily-fluid spills | about 5,000 ppm |
Example Problems
Example 1. You have regular household bleach at 6 percent and want 1 liter (1,000 mL) of a 1,000 ppm disinfecting solution. Convert the target: 1,000 ppm equals 0.1 percent. The bleach volume is V_1 = (0.1 x 1000) / 6 = 16.67 mL. The water to add is 1000 – 16.67 = 983.33 mL.
Example 2. You mixed 25 mL of 8.25 percent bleach into enough water to make 500 mL total. The final concentration is C_2 = (8.25 x 25) / 500 = 0.4125 percent, which is 4,125 ppm.
Frequently Asked Questions
What concentration should I use to disinfect? Around 600 to 1,000 ppm is common for general hard-surface disinfecting, while food-contact surfaces usually call for about 200 ppm. Follow the guidance for your specific application.
Why do I enter percent for the stock bleach? The sodium hypochlorite percentage on the bottle is the stock concentration C_1. Entering it lets the calculator scale the dose to whatever target you choose in percent or ppm.
Can I mix the solution ahead of time? It is best to mix diluted bleach fresh. Available chlorine breaks down over time, and exposure to light and heat speeds the loss, so an old batch will be weaker than the calculated value.