Bleach Dilution Calculator
Enter your bleach bottle strength and the final solution size, then choose a target concentration as a percentage, ppm value, or dilution ratio. The calculator tells you exactly how much bleach to add and how much water to top up with, shows step-by-step math, and maps your result against CDC-aligned use-case ranges from food-contact sanitizing all the way to C. difficile sporicidal levels.
How bleach dilution works
Bleach is sold as a concentrated solution of sodium hypochlorite (NaOCl) in water, typically 5.25%, 6%, or 8.25% for household products and up to 12.5% for commercial or pool grades. To disinfect safely and effectively you dilute the stock solution to a working concentration measured in parts per million (ppm) of free available chlorine. The calculation uses the conservation-of-mass principle: the amount of chlorine you start with equals the amount in the final solution. Written as a formula, C1 x V1 = C2 x V2, where C1 is the stock concentration, V1 is the volume of stock bleach, C2 is the target concentration, and V2 is the total final volume. Rearranging gives V1 = (C2 / C1) x V2, the volume of bleach to add. The rest of the final volume is topped up with water.
Choosing the right concentration for your task
The appropriate bleach concentration depends on what you are trying to disinfect and what level of pathogen kill is required. Food-contact surfaces such as cutting boards and countertops in commercial kitchens are sanitized at 100-200 ppm, which is low enough that rinsing is often optional under FDA guidelines. Routine household or healthcare surface disinfection is typically done at 500-1000 ppm, which kills the common bacteria and viruses including influenza, norovirus, and SARS-CoV-2 with about one minute of contact time. High-risk situations such as blood or body-fluid spills, or environments where Clostridium difficile spores are a concern, call for 5000 ppm (a 1:10 dilution of 5.25% bleach), applied for at least two to ten minutes on a pre-cleaned surface. Emergency water treatment uses a much lower dose, about 8 ppm, because the water is being consumed and excess chlorine is toxic.
Safety, stability, and storage
Diluted bleach solution degrades rapidly. At room temperature, a 1000 ppm working solution loses roughly half its available chlorine within 24 hours, and may be essentially inactive after 48 hours. Always prepare fresh solution daily and label it with the date and time of mixing. Store stock bleach in a cool, dark location; heat and ultraviolet light accelerate decomposition. Never mix bleach with ammonia (forms toxic chloramine gas), acids such as vinegar or toilet cleaners (releases chlorine gas), or rubbing alcohol (forms chloroform and other hazardous compounds). Always add bleach to water, not water to bleach, to minimize splashing. Wear gloves, eye protection, and work in a well-ventilated area when preparing concentrated solutions above 1000 ppm. For regulated food-service or healthcare environments, verify the final concentration with a free chlorine test strip after mixing.
Metric and imperial conversions for practical mixing
Most bleach protocols give measurements in tablespoons, teaspoons, cups, or fluid ounces rather than millilitres, because those are the utensils people have. One tablespoon is about 14.8 mL; one teaspoon is about 4.9 mL; one cup is about 236.6 mL; one US fluid ounce is about 29.6 mL; one US gallon is 3785 mL. A classic CDC general-disinfection recipe for 5.25% bleach is 4 teaspoons (about 20 mL) per 32 fl oz (about 946 mL) of water, which yields roughly 1000 ppm. The calculator works in mL, L, fl oz, or gallons so you can match your preferred measuring tools.
CDC-aligned bleach concentration guide
| Use case | Target ppm | Approx. ratio (1:x) | % NaOCl | Contact time |
|---|---|---|---|---|
| Food-contact sanitizing | 100-200 ppm | 1:250 to 1:500 | 0.01-0.02% | 1 min |
| Routine surface disinfection | 500-600 ppm | 1:80 to 1:100 | 0.05-0.06% | 1 min |
| General disinfection | 1000 ppm | ~1:50 | 0.10% | 1-2 min |
| Blood / body-fluid spills | 5000 ppm | ~1:10 | 0.50% | 2-5 min |
| C. difficile sporicidal protocol | 5000+ ppm | 1:10 | 0.50% | 10 min |
| Emergency water treatment* | 8 ppm | ~1:6500 | ~0.0008% | 30 min |
| Mold remediation | 1000-5000 ppm | 1:10 to 1:50 | 0.10-0.50% | 5-10 min |
Recommended free available chlorine (FAC) ranges by use case, using 5.25% household bleach as stock. Always pre-clean surfaces before disinfecting.
Frequently asked questions
What is the bleach-to-water ratio for general disinfection?
For general disinfection with standard 5.25-6% household bleach, a common guideline is 4 teaspoons of bleach per 32 fl oz (1 quart) of water, yielding roughly 1000 ppm free available chlorine. That equates to approximately a 1:50 dilution. Always pre-clean the surface, apply the solution, and allow at least one to two minutes of contact time before rinsing or wiping.
How do I convert bleach concentration from ppm to percent?
Divide the ppm value by 10,000 to get the percentage. For example, 1000 ppm equals 0.10%, 500 ppm equals 0.05%, and 5000 ppm equals 0.50%. Going the other way, multiply the percentage by 10,000 to get ppm. This relationship holds because 1% = 10,000 mg/L = 10,000 ppm for dilute aqueous solutions.
How long does a diluted bleach solution stay effective?
Diluted bleach degrades significantly within 24 hours at room temperature, losing roughly half its available chlorine. Sunlight and heat speed up that loss further. Always prepare fresh solution the same day you intend to use it, and discard any unused solution at the end of the day. If you need to verify potency, use a free chlorine test strip before applying in a critical setting.
What concentration of bleach kills viruses like SARS-CoV-2?
Studies and regulatory guidance (including EPA List N) support that 500-1000 ppm free available chlorine, applied for at least one minute on a pre-cleaned non-porous surface, is effective against SARS-CoV-2, influenza, and most common pathogens. For harder-to-kill organisms such as norovirus, 1000 ppm with two minutes of contact time is recommended. For C. difficile spores, 5000 ppm for ten minutes is the standard sporicidal protocol.
Can I use any bleach? Does concentration on the label matter?
Yes, the label concentration matters significantly. Regular household bleach is typically 5.25-6% sodium hypochlorite; concentrated or "ultra" bleach is often 8.25%; commercial grades and pool bleach can reach 10-12.5%. Using the wrong starting concentration will give you the wrong working concentration. Always check the label and enter the exact percentage into the calculator. Scented bleaches and "splash-less" bleaches may contain stabilisers or surfactants that make them unsuitable for food-contact or drinking-water applications.