Bleach Dilution Calculator

What the percentage on the bottle means

The number on a bleach label is the strength of the sodium hypochlorite inside, and it is the only thing that makes one dilution recipe different from another. Regular household bleach is 5.25%, the concentrated versions run 6.0% to 8.25%, and some store brands sit near 3.0%. A splashless or scented bottle may list a different strength again, which is why the first step is always to read the label rather than assume.

Percent converts to parts per million by moving the decimal four places. A 5.25% solution is 52,500 ppm of available chlorine, 6.0% is 60,000 ppm, 8.25% is 82,500 ppm, and 3.0% is 30,000 ppm. Those numbers are what the dilution math runs on, and they are also what a test strip reads.

Strength fades with time. An unopened bottle keeps most of its chlorine for about a year, and an opened bottle stored in a hot garage can lose half of it in six months. If the bottle is old, the label is optimistic and the mix will be weaker than the math predicts. That is one reason public health guidance tells you to follow the label directions first and treat any homemade recipe as a fallback.

The ppm math behind every dilution

One formula covers every job on this page. Multiply the target concentration by the volume of water, then divide by the concentration in the bottle.

Ounces of bleach = target ppm x ounces of water / ppm in the bottle.

Water is the easy part: 1 gallon is 128 fluid ounces, 1 quart is 32, and 1 cup is 8. A 5.25% bottle holds 52,500 ppm, so a target of 1,000 ppm in a gallon works out to 1,000 x 128 / 52,500, which is 2.44 ounces. The same formula handles a quart, a bucket or a spray bottle, and it handles any bottle strength without a new chart.

The dilution ratio falls out of the same numbers. Divide the water volume by the bleach volume and you get the parts of water per part of bleach. 128 divided by 2.44 is 52, so the mix is 1 part bleach to 52 parts water. That is the number people quote when they say a 1:50 solution, and it is why a 1:10 mix is roughly five times stronger than a 1:50 mix.

Worked example: one gallon at 1,000 ppm

This is the standard disinfecting solution for hard, non-porous surfaces, and the one the CDC bleach guidance describes as 5 tablespoons of bleach per gallon of room temperature water, or 4 teaspoons per quart.

• Target: 1,000 ppm in 128 ounces of water.
• Bottle: 5.25%, which is 52,500 ppm.
• Bleach: 1,000 x 128 / 52,500 = 2.44 ounces.
• In kitchen measures: 4.9 tablespoons, so 5 tablespoons, which is a scant 1/3 cup.
• Ratio: 1 part bleach to 52 parts water.

Five tablespoons is 2.5 ounces rather than 2.44, which lands the mix at about 1,025 ppm. That is inside the range a test strip can distinguish, so it is close enough for a countertop. If you are mixing for a facility and reporting numbers, measure in ounces and use the exact figure.

Run the same formula at 5,000 ppm, the strength used for blood and other body fluid spills, and you get 12.19 ounces per gallon. That is 1 1/2 cups, or a 1:10 mix, and it is five times the chlorine of the surface solution. Run it at 200 ppm for food-contact sanitizing and you get 0.49 ounces, which is 1 tablespoon per gallon and a 1:262 mix.

Dilutions by job

Different jobs need different concentrations, and using a stronger mix than the job needs wastes bleach, smells worse and damages surfaces faster. The three levels below cover almost everything a household does.

The 200 ppm level is for surfaces that touch food, and it needs a clean surface first, because bleach is inactivated by dirt and grease. The 1,000 ppm level is the general disinfecting strength for counters, sinks, doorknobs and bathroom fixtures after an illness. The 5,000 ppm level is for spills of blood, vomit or feces, and it is also the strength hospitals use for a heavily contaminated surface.

Laundry is a separate case and does not follow ppm the same way. A normal load takes 3/4 cup of 5.25% bleach added to the wash water, with the detergent, never poured directly on fabric. Check the care label first, since bleach ruins wool, silk, mohair and anything labeled dry clean only.

Adjusting for a stronger bottle

Concentrated bleach is sold as a smaller bottle that does the same work, and the trap is using the old 5.25% recipe with an 8.25% product. The result is a mix that is 57% too strong, which is hard on surfaces and harsh in the air.

The pattern is simple: stronger bottle, less product, larger ratio number. Doubling the strength halves the amount you need. A 3.0% bottle needs 4.27 ounces for the same gallon, which is more than most people would guess, and it is the reason a weak store brand can feel like it does nothing.

The Clorox dilution chart prints the same arithmetic for every product in its line, and the numbers agree with the formula above once the bottle strength is accounted for.

If the label gives a range rather than a single figure, use the low end for a first mix and check with a test strip. Strips are sold in pool and janitorial sections, cost a few dollars for a tube, and read 0 to 2,000 ppm on the low range. They are the only way to know what is in the bucket, since an old bottle may hold less chlorine than the label promised.

Never mix bleach with these

Bleach reacts with a long list of household products, and a few of those reactions produce gas that will put you on the floor. The rule is simple: bleach and water, nothing else, and never in the same bucket as another cleaner.

The ammonia case is the one that catches people, because ammonia hides in window cleaner, floor polish, urine and some stainless steel polishes. A bathroom cleaned with an ammonia product and then with bleach can produce chloramine gas in a small, poorly ventilated room within minutes. Symptoms are coughing, chest tightness, watery eyes and trouble breathing, and they can start before you notice a smell.

The acid case is just as common. Vinegar is a popular natural cleaner, and mixing it with bleach releases chlorine gas, the same gas used in chemical warfare. Toilet bowl cleaners are usually acidic too. If you have already mixed them, do not try to fix the bucket. Open a window, leave the room, and call Poison Control if anyone has symptoms.

How to mix and use it safely

Mix in a ventilated space with the window open or the exhaust fan running. Use cold or room temperature water, because hot water breaks down the hypochlorite faster and releases more vapor. Add the bleach to the water rather than the water to the bleach, which keeps splashing down and mixes more evenly.

Wear gloves, and glasses if you are mixing more than a quart. Bleach splashed in the eye is a chemical burn, and the first response is 15 minutes of plain water and a call to a doctor. Keep the bottle out of reach of children and never transfer a mix into a drink bottle or a spray bottle that once held something else.

Let the solution sit for the contact time on the label, which is 1 minute for many household disinfectants and 10 minutes for some. Then wipe or let it air dry. Do not rinse a food-contact surface with the 1,000 ppm mix, but do rinse or air dry a 200 ppm sanitizer before the surface touches food.

Mix only what you will use the same day. Chlorine evaporates and the solution loses strength within 24 hours, so a bucket left overnight is mostly salt water. Never store a mixed solution in a sealed container, since the gas builds pressure, and never put leftover mix back in the bleach bottle.

Surfaces and materials that should not get bleach

Bleach is a strong oxidizer, and it does not care whether the surface can take it. Natural stone such as granite, marble and travertine etches and dulls. Sealed wood loses its finish. Wool, silk, mohair, leather and anything labeled dry clean only can be yellowed or dissolved. Colored fabrics fade, and some print inks run.

Stainless steel is the surprise on the list. A short contact time is fine, but leaving a bleach solution to sit on stainless pits the surface and can leave rust spots, because the chloride attacks the protective chromium layer. Rinse and dry stainless after a bleach wipe. Aluminum and copper react the same way.

For mold on a porous surface such as drywall or grout, bleach kills what it touches but does not reach the roots below the surface, and the EPA guidance on bleach and mold says the priority is fixing the moisture that let the mold grow. Clean the surface, dry it, and address the leak. On a porous material, a detergent and water scrub often does more than a stronger bleach mix.