Bleach Dilution Calculator — ppm Available Chlorine

Background.

Product directions, health guidance and pool manuals usually give a chlorine target in ppm of available chlorine, while the bottle under the sink gives a percentage, often of something else. Getting from one to the other takes two conversions before any diluting starts.

The first is units. One percent is 10,000 ppm, or 10,000 mg per litre, so a 0.1% target is 1,000 ppm. The second is what the percentage on the label measures. American household bleach is usually labelled as % sodium hypochlorite, while industrial, pool and many European products state % available chlorine, and the two are not the same number. Available chlorine is counted as the equivalent weight of chlorine gas, and because a molecule of sodium hypochlorite is heavier than one of Cl₂, every 1% of sodium hypochlorite is worth 0.95246% available chlorine. Read 8.25% sodium hypochlorite as 8.25% available chlorine and every solution you mix comes out about 4.75% weaker than intended.

Once the bottle's strength is in ppm of available chlorine, the rest is the ordinary dilution rule: the chlorine you pour out of the bottle is all the chlorine in the bucket.

The target itself has to come from your product's label or your local public-health authority. In the United States chlorine disinfectants are registered pesticides, and their labels are the legal instructions for concentration and contact time. And whatever the strength, never mix bleach with ammonia or with acids, and work with good ventilation.

What is bleach dilution calculator (ppm available chlorine)?

Available chlorine expresses the oxidising strength of a hypochlorite solution as the mass of chlorine gas, Cl₂, that would do the same oxidising work, conventionally measured by how much iodine the solution frees from acidified iodide. One mole of sodium hypochlorite does the same work as one mole of Cl₂, so a percentage of NaOCl converts to available chlorine by the ratio of their molar masses, 70.90 ÷ 74.4388.

How to use this calculator.

1. 01Find the strength on your bottle and select what it measures: '% sodium hypochlorite', usual on US household bleach, or '% available chlorine' (sometimes '% active chlorine').
2. 02Enter that percentage as written, 8.25 rather than 0.0825. An old or long-opened bottle may be weaker than its label.
3. 03Enter the target in ppm of available chlorine from your product's directions; if they give a percentage, multiply it by 10,000.
4. 04Enter the amount of finished solution in litres (a US gallon is 3.785 L), then measure out the bleach and add water up to that total, in a well-ventilated space and with nothing else in the container.

The formula.

The bottle's strength is first turned into ppm of available chlorine: C_stock = strength (%) × f × 10,000, where f = 1 for an available-chlorine label and f = M(Cl₂) ÷ M(NaOCl) for a sodium hypochlorite label. Using the IUPAC standard atomic weights (chlorine 35.45, sodium 22.98976928, oxygen 15.999), M(Cl₂) = 70.90 g/mol and M(NaOCl) = 74.4388 g/mol, so f = 0.95246. The dilution rule C_stock × V_bleach = C_target × V_final then gives V_bleach = C_target × V_final ÷ C_stock, and the water is V_final − V_bleach, treating the two volumes as simply adding together. The dilution factor is V_final ÷ V_bleach, and the parts of water per part of bleach is one less. A target stronger than the bottle is refused, since dilution cannot raise a concentration; that error usually means a percentage was typed where ppm was expected, or the wrong label basis was chosen. Storage decay, pH, and chlorine used up by dirt on a surface are not modelled.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Commission on Isotopic Abundances and Atomic Weights (CIAAW), International Union of Pure and Applied Chemistry. Standard atomic weights — the table based on the Atomic Weights 2021 report with revisions completed in 2024. Chlorine [35.446, 35.457] (conventional value 35.45); sodium 22.989 769 28(2); oxygen [15.999 03, 15.999 77] (conventional value 15.999). These give M(Cl₂) = 70.90 g/mol and M(NaOCl) = 74.438 769 g/mol, and hence the available-chlorine conversion factor 0.952 460 669 2 used on this page. Independent standards body; open access; retrieved and values confirmed 2026-07-29.
2. [2]US Environmental Protection Agency. 40 CFR §156.10(i)(2)(ii), Labeling requirements — Contents of Directions for Use: 'Immediately below the statement of use classification, the statement "It is a violation of Federal law to use this product in a manner inconsistent with its labeling."' This is why this page states a target concentration only as a user input and never as a recommendation. Current eCFR text retrieved and quoted 2026-07-29.
3. [3]US Environmental Protection Agency. 40 CFR §156.10(i)(2)(v)–(vi), which requires a registered pesticide label to state 'the dosage rate associated with each site and pest' and 'the method of application'. Cited to make explicit where a user should obtain the target concentration and contact time this calculator deliberately does not supply. Current eCFR text retrieved 2026-07-29.
4. [4]International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (the 'Gold Book'), 5th edition, online version 5.0.0 (2025), entry 'amount concentration, c' (A00298): the definition of concentration as amount of solute per volume of solution that the percent-to-ppm conversion builds on. The equivalence 1 % w/v = 10 g/L = 10 000 mg/L = 10 000 ppm in dilute aqueous solution is straightforward unit arithmetic, not a quotation from the entry. Open access.