Calculate stock bleach volume for a dilution or the concentration of a known mix. Choose the stock percentage basis; mass percentages require product-specific density. Follow the product label for disinfection.
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 approximate water volume is the difference below; for a specified final volume, add water to that final volume rather than relying on exact volume additivity:
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
C_1 and C_2 must describe the same substance on the same mass-per-volume basis. V_1 is stock volume and V_2 is measured final volume. For stock mass percent (w/w), the calculator requires density and converts to g/L. For mass/volume percent (w/v), 1% equals 10,000 mg/L. Mass ppm is approximately mg/L only for dilute final solutions near 1 g/mL. Sodium hypochlorite and available chlorine are different reporting bases and are not converted here.
Bleach Strengths and Disinfection Targets
The product strengths below are illustrative ranges, not defaults. Check the actual label and its concentration basis; strength varies and declines with age. Follow the product label for dilution, target, contact time, surface compatibility and protection. Never mix bleach with other cleaners.
| 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 | Follow the registered product label |
| General hard-surface disinfecting | Follow the registered product label |
| Heavy disinfection of bodily-fluid spills | Follow the registered product label |
Example Problems
Example 1. As a mathematical example, assume stock concentration is 6% w/v and target is 1,000 mg/L of the same substance, with a final volume of 1 liter (1,000 mL). This is not a recommended disinfection target. Convert the target: 1,000 mg/L equals 0.1% w/v. The bleach volume is V_1 = (0.1 x 1000) / 6 = 16.67 mL. The approximate water volume is 1000 – 16.67 = 983.33 mL; dilute to the specified final volume.
Example 2. Assume stock is 8.25% w/v. You mixed 25 mL into enough water to make 500 mL total. The final concentration is C_2 = (8.25 x 25) / 500 = 0.4125% w/v, which is 4,125 mg/L (approximately 4,125 mass ppm only near 1 g/mL).
Frequently Asked Questions
What concentration should I use to disinfect? Use the registered product label or authoritative guidance for the exact product, organism, surface and contact time. This calculator does not select or validate a disinfection target.
Why do I enter percent for the stock bleach? Enter the labeled stock strength and choose w/w or w/v. Mass percent requires product-specific density before applying a volume dilution equation. Use the same reported substance for the target; available chlorine and sodium hypochlorite are not interchangeable.
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.
