Bleach Disinfecting Ratio Calculator
How much household bleach to add to water to disinfect, sanitize food-contact surfaces, clean up norovirus, flood damage or mold, or treat emergency drinking water — scaled to your bleach strength (5.25–12.5%), with the mixing ratio, ppm, contact time and a recipe for every container size.
How it works
Bleach = recipe rate × (5.25 ÷ your bleach %) × water volume · Recipe rates per gallon of water at 5.25%: disinfect 5 tbsp (≈1,000 ppm), food-contact sanitize 1 tbsp (≈200 ppm), norovirus 25 tbsp (≈5,000 ppm), flood clean-up 3.2 tbsp (1 cup per 5 gal), mold 16 tbsp (1 cup) · Drinking water: 8 drops of 6% bleach per gallon, doubled for cloudy or cold water · Custom: bleach (mL) = ppm × water (mL) ÷ (bleach % × 10,000 − ppm) · Strength (ppm) = bleach mL × % × 10,000 ÷ total mL
Household bleach is a solution of sodium hypochlorite, and what kills germs is how much of it ends up in the bucket — usually given in parts per million (ppm). The CDC recipes are written for regular 5–9% bleach: 5 tablespoons (a third of a cup) per gallon of water for general disinfecting, about 1,000 ppm; 1 tablespoon per gallon for surfaces that touch food, about 200 ppm, which can air-dry without rinsing; and 5 to 25 tablespoons per gallon (1,000–5,000 ppm) after norovirus. Flood clean-up uses 1 cup per 5 gallons for hard items and food cans, and EPA’s emergency drinking-water dose is just 8 drops of 6% bleach per gallon. Stronger products such as 8.25% concentrated bleach or 10–12.5% pool chlorine carry more active ingredient per spoonful, so the calculator scales the dose by the strength ratio to keep the same ppm, then shows the result in tablespoons, teaspoons, cups, millilitres and drops, the mixing ratio, the strength of the finished mix, the contact time and a recipe for spray bottles and buckets. Diluted bleach loses strength within a day, and it must never be mixed with ammonia, vinegar or other cleaners.
Worked example
To disinfect with regular 5.25% bleach in 1 gallon of water: 5 × (5.25 ÷ 5.25) × 1 = 5 tablespoons (about 74 mL, or ¼ cup + 1 tbsp). That is 1 part bleach to about 51 parts water and works out at roughly 1,000 ppm. With 8.25% concentrated bleach the dose drops to 5 × (5.25 ÷ 8.25) ≈ 3.2 tablespoons, and a 32 fl oz spray bottle needs about 1¼ tablespoons of regular bleach. For norovirus, the same gallon takes 25 tablespoons (about 1⅔ cups), and to treat a gallon of clear drinking water with 6% bleach you add just 8 drops.
Sources: CDC — Cleaning and disinfecting with bleach · CDC — How to safely clean and sanitize with bleach after a disaster · CDC — How to prevent norovirus · U.S. EPA — Emergency disinfection of drinking water · CDC — Preparing chlorine solutions (Appendix E)
Frequently asked questions
How much bleach do I mix with a gallon of water to disinfect?
For regular 5–6% bleach, 5 tablespoons (a third of a cup) per gallon, or 4 teaspoons per quart. That gives about 1,000 ppm. Keep the surface wet for at least a minute, or the time on the label, after cleaning off any dirt.
What is the bleach ratio for sanitizing dishes and food-prep surfaces?
About 1 tablespoon of regular bleach per gallon of water, roughly 200 ppm. Wash and rinse first, then wipe or soak and let it air-dry. At 200 ppm or less no rinse is needed; stronger mixes should be rinsed off before the surface touches food.
How much bleach kills norovirus?
CDC recommends 1,000 to 5,000 ppm — 5 to 25 tablespoons of 5–8% bleach per gallon — left on the surface for at least 5 minutes. Choose the norovirus option for the 5,000 ppm end, which suits vomit and diarrhea clean-up.
Does concentrated bleach need less?
Yes. 8.25% bleach has more sodium hypochlorite per spoonful, so about 3.2 tablespoons per gallon gives the same 1,000 ppm as 5 tablespoons of 5.25% bleach. Pick your strength from the list or type the % on the label.
How much bleach do I add to drinking water in an emergency?
EPA says 8 drops of 6% bleach (6 drops of 8.25%) per gallon of clear water, or twice that if the water is cloudy, colored or very cold. Stir, wait 30 minutes and check for a slight chlorine smell. Use plain, unscented bleach under a year old.
How long does a bleach solution last?
Make a fresh batch every day. Diluted bleach weakens within about 24 hours, faster in sunlight and heat, so a spray bottle mixed last week may no longer disinfect.
Can I mix bleach with vinegar or other cleaners?
No. Bleach with vinegar or other acids releases chlorine gas, and bleach with ammonia releases chloramine — both can seriously injure your lungs. Use bleach only with plain water and rinse surfaces between products.
Related calculators
General guidance only — follow your product label and never mix bleach with ammonia or acidic cleaners.