Bleach Dilution Calculator - Water-to-Bleach Ratios

What is a bleach dilution calculator?

A bleach dilution calculator works out how much water to add to a given amount of bleach to reach a target dilution ratio, such as 1:10. Diluting bleach with water makes a weaker cleaning or disinfecting solution that is safer to use and cheaper than using bleach at full strength.

What a dilution ratio means

A dilution ratio like "1:10" describes the finished solution, not just the water. The first number is the bleach. The second number is the total number of parts in the mixed solution. A 1:10 ratio means 1 part bleach plus 9 parts water, for 10 parts total. The finished solution is one-tenth as strong as the original bleach.

A higher second number means a weaker solution. A 1:100 mix has less bleach in it than a 1:10 mix.

How to calculate bleach dilution (the formula)

The calculator uses one formula to find the water needed:

Once the water volume is known, two more values follow from it:

"Bleach Volume" is the amount of bleach the user starts with. "Dilution Ratio" is the total number of parts in the target ratio (10 for a 1:10 mix, 100 for a 1:100 mix). Both amounts must use the same unit, such as millilitres or ounces.

Worked example

To dilute 100 ml of bleach to a 1:10 ratio:

• Water Volume = 100 × (10 − 1) = 100 × 9 = 900 ml
• Total Volume = 100 + 900 = 1,000 ml
• Bleach Percentage = 100 ÷ 10 = 10%
• Water Percentage = 90%

The result is 1,000 ml of solution: 100 ml bleach and 900 ml water.

Common dilution ratios

The calculator offers four one-tap ratios, alongside a custom ratio option for any other value:

Stronger mixes (1:10) are typically used for general household disinfecting, such as bathroom surfaces. Weaker mixes (1:50 or 1:100) are typically used where a lighter touch is wanted, such as sanitizing after a surface has already been cleaned. Product labels and local health guidance should be checked for the specific ratio a task requires, since recommendations vary by country and by use case.

How to use the calculator

1. Enter the amount of bleach available.
2. Choose a unit: millilitres, litres, ounces, or cups.
3. Pick a ratio (1:10, 1:20, 1:50, 1:100) or check "Custom Ratio" and type a different value.
4. Read the water amount, the total finished volume, and a bar showing the bleach-to-water split.
5. Use the copy button to copy the water amount.

The "Reset" button restores the starting values of 100 ml bleach at a 1:10 ratio.

Safety when diluting bleach

• Add bleach to water, not water to bleach. Pouring water into bleach can cause splashing of concentrated bleach.
• Work in a ventilated area. Diluted bleach still gives off chlorine fumes.
• Never mix bleach with ammonia or with acidic cleaners such as vinegar. Both combinations release toxic chlorine-based gas.
• Wear gloves. Bleach can irritate or dry out skin.
• Label containers with the ratio and the date, since diluted bleach looks like water.
• Household bleach is usually sold at a sodium hypochlorite concentration between about 5% and 8.25%. The percentage is printed on the bottle and can affect how strong a given ratio ends up being.

Frequently asked questions

How long does diluted bleach stay effective? Diluted bleach loses strength quickly. Light, air, and heat break down the active chlorine, so a solution mixed a day or more ago may no longer disinfect reliably. Mixing a fresh batch for each use is the safest approach.

Can bleach be mixed with other cleaning products? No. Mixing bleach with ammonia produces toxic chloramine gas. Mixing bleach with vinegar or other acids produces toxic chlorine gas. Surfaces cleaned with another product should be rinsed with plain water before bleach is applied.

Why does the water amount depend on the ratio and not just the bleach amount? Because the ratio sets how many total parts the finished solution should have. The formula multiplies the bleach amount by one less than the ratio, since the bleach itself is already one of those parts.

Does bleach kill all germs? No. Bleach is effective against many bacteria and viruses, but some organisms, such as the parasite Cryptosporidium, are resistant to chlorine. Bleach also works less well on porous surfaces like unsealed wood, and less well when dirt or organic matter is still on the surface.

What if my bleach is a different concentration than usual? The calculator's ratio-based formula assumes a normal household bleach concentration. For a solution built around a specific percentage rather than a ratio, the amount of bleach needed is: Target Volume × (Target Concentration ÷ Original Concentration). For example, to make 1 L of a 0.5% solution from 10% bleach: 1 L × (0.5% ÷ 10%) = 0.05 L, or 50 ml of bleach topped up with water to 1 L.

Which surfaces should not be cleaned with bleach? Bleach can corrode metals such as aluminium, etch natural stone like marble, discolor wood finishes, and damage some plastics and painted surfaces. A milder cleaner is usually a better choice for these materials.