Audited —·Last updated 29 Jul 2026·4 citations·Tier 3·0 uses

Bleach Dilution Calculator — ppm Available Chlorine

Work out how much bleach and how much water to mix for a target ppm of available chlorine, converting correctly between % sodium hypochlorite and % chlorine.

Bleach Dilution Calculator (ppm Available Chlorine)

What does the number on your bottle mean?
The percentage printed on the label, as a number: 8.25 % is 8.25, not 0.0825. Note that hypochlorite decays in storage — the label figure is a manufacture-date value, so an old bottle is weaker than it says.
%
The concentration YOU need, in ppm of available chlorine (equivalently mg/L). 1 % = 10 000 ppm. This calculator does not recommend a value — take it from the directions on your product's registered label.
ppm
Total volume of the mixed solution, in litres. 1 US gallon = 3.785 L; 1 imperial gallon = 4.546 L; a 5 L bucket is 5.
L
Bleach to measure out
12.7262
Volume of undiluted stock bleach. Add this to water to make up the total volume you asked for. 5 mL is one teaspoon, 15 mL one tablespoon, 240 mL one US cup.
Water to add
987.2738 mL
Dilution factor (1 in N)
78.578
Parts water per part bleach
77.578
Available chlorine in the undiluted bleach
78,578.0052 ppm
Available chlorine in the undiluted bleach
7.8578 %
Target, as a percentage
0.1 %
Mixing ratio, stated unambiguously
1 part bleach in 78.6 parts of finished solution — that is 1 part bleach plus 77.6 parts water

Background.

This calculator works out how much bleach and how much water to combine to reach a target concentration of available chlorine. It is the dilution law C₁V₁ = C₂V₂ carried in the units bleach is actually sold and specified in, plus the two conversions a general dilution calculator cannot do for you.

The first conversion is percent to ppm: one percent weight-per-volume is 10 000 ppm, which is also 10 000 mg/L. The second is the one that catches people. A bottle labelled '8.25 % sodium hypochlorite' does not contain 8.25 % available chlorine. Available chlorine is conventionally expressed as the equivalent mass of Cl₂, and one mole of NaOCl is equivalent to one mole of Cl₂, so the conversion factor is the ratio of their molar masses: 70.90 ÷ 74.4388 = 0.95246. That makes 8.25 % sodium hypochlorite equal to 7.858 % available chlorine — 4.75 percent lower. Industrial, pool and many European labels quote available chlorine directly, so the page asks which basis your bottle uses before it does anything else.

**This page does not tell you what concentration to use, and nothing here is a disinfection recommendation.** Chlorine-based disinfectants sold in the United States are regulated as pesticides, and 40 CFR §156.10(i) requires every registered label to carry the statement 'It is a violation of Federal law to use this product in a manner inconsistent with its labeling.' Take your target concentration, contact time and surface from the directions on your own product's label or from your local public-health authority. What this calculator provides is the arithmetic that gets you from that target to a measuring jug.

Two further limits worth knowing. Hypochlorite solutions decay in storage, faster when warm or exposed to light, so the percentage printed on the bottle is a manufacture-date value and an old bottle is weaker than it claims — if the result matters, test the mixed solution with chlorine test strips rather than trusting the label. And the ratio outputs are given in both conventions, because '1:10' is used in the wild to mean both 'one part in ten of finished solution' and 'one part bleach to ten parts water', and those differ by ten percent.

What is bleach dilution calculator (ppm available chlorine)?

Available chlorine is a measure of the oxidising power of a chlorine-based disinfectant, expressed as the mass of elemental chlorine (Cl₂) that would have the same oxidising capacity — conventionally, that would liberate the same amount of iodine from an acidified iodide solution. It is quoted either as a percentage by weight-per-volume or in parts per million, which for a dilute aqueous solution is the same as milligrams per litre. Sodium hypochlorite, the active ingredient of liquid bleach, reacts mole-for-mole with iodide in the same way Cl₂ does, so one mole of NaOCl carries the same available chlorine as one mole of Cl₂. Because NaOCl has the larger molar mass — 74.4388 g/mol against 70.90 g/mol, from the IUPAC/CIAAW standard atomic weights — a given mass of NaOCl carries only 70.90/74.4388 = 0.95246 times its own mass in available chlorine. This is why a label figure expressed as '% sodium hypochlorite' must be multiplied by 0.95246 before it can be compared against a target expressed in ppm available chlorine, and why the two bases are not interchangeable. Everything else on this page is the ordinary dilution law: the amount of available chlorine in the bleach you measure out equals the amount in the finished solution, so C_stock × V_bleach = C_target × V_final.

How to use this calculator.

  1. Read your bottle and select the matching basis: '% sodium hypochlorite' or '% available chlorine'. If the label says 'sodium hypochlorite ... 8.25 %' in an ingredients panel, that is the first one.
  2. Enter the label percentage as a plain number — 8.25 %, not 0.0825.
  3. Enter your target concentration in ppm of available chlorine, taken from the directions on your product's label. 1 % = 10 000 ppm, so 0.1 % is 1000 ppm.
  4. Enter how much finished solution you want, in litres. 1 US gallon = 3.785 L.
  5. Measure out the stated volume of bleach, then add water up to the total volume. Read the mixing-ratio line if you would rather work in parts than in millilitres.
  6. If accuracy matters, verify the mixed solution with chlorine test strips — an opened or old bottle is weaker than its label.

The formula.

C_stock · V_bleach = C_target · V_final
C_stock · available chlorine in the bleach, ppmC_target · target available chlorine, ppmV_bleach · volume of bleach to measure outV_final · total volume of finished solutionC_stock = strength(%) × f × 10 000f · 1 for an available-chlorine labelf · 0.95246 = M(Cl₂)/M(NaOCl) for a NaOCl label

Two steps. First convert the label strength into ppm of available chlorine:

C_stock (ppm) = strength (%) × f × 10 000

where f = 1 if the label already quotes available chlorine, and f = M(Cl₂)/M(NaOCl) = 70.90 / 74.438769 = 0.9524606692 if it quotes sodium hypochlorite. The molar masses come from the IUPAC/CIAAW standard atomic weights (Atomic Weights 2021, table revised 2024): Cl 35.45, Na 22.98976928, O 15.999.

Then apply the dilution law, which is just conservation of the chlorine:

V_bleach = C_target × V_final / C_stock V_water = V_final − V_bleach

Rounding stage: FINAL ONLY. Every step is carried at 30-digit Decimal.js precision with a single rounding to ten decimal places at the return boundary; nothing is rounded in between, and the conversion factor is computed from the atomic weights rather than hard-coded as 0.9525.

Worked through with the defaults: 8.25 % sodium hypochlorite × 0.9524606692 = 7.857800521 % available chlorine = 78 578.005 ppm. For 1000 ppm in 1.000 L, V_bleach = 1000 × 1.000 / 78 578.005 = 0.0127262 L = 12.7262 mL, leaving 987.274 mL of water. The dilution factor is 1000/12.7262 = 78.58, so this is a '1 in 78.6' dilution, which is 1 part bleach plus 77.6 parts water.

Invalid domain. Strength must be greater than 0 % and at most 100 %. The target must be positive and cannot exceed the stock's own available chlorine — diluting cannot raise a concentration, and if you get that error the usual cause is confusing percent with ppm, or having selected the wrong label basis. The final volume must be positive. Every rejection names the field.

What is not modelled: hypochlorite decay in storage, the pH dependence of the hypochlorous-acid/hypochlorite equilibrium that actually governs biocidal activity, chlorine demand from organic soil on the surface being treated, and any interaction with other cleaning products. Never mix bleach with an acid or with ammonia.

A worked example.

Example

You have a bottle of US household bleach whose ingredients panel reads 'sodium hypochlorite 8.25 %', and a label direction that calls for 1000 ppm of available chlorine. You want to make up one litre. Select the sodium-hypochlorite basis and enter 8.25, 1000 and 1. The calculator first converts the label figure: 8.25 % × 0.9524606692 = 7.857800521 % available chlorine, which is 78 578.005 ppm. Then it applies the dilution law: V_bleach = 1000 ppm × 1.000 L ÷ 78 578.005 ppm = 12.7262 mL, so you measure out 12.73 mL of bleach — a shade under a tablespoon — and make it up to 1000 mL with 987.27 mL of water. The mixing-ratio line reads '1 part bleach in 78.6 parts of finished solution — that is 1 part bleach plus 77.6 parts water'. Both numbers are given because writing this as '1:78' would be ambiguous. If you had skipped the conversion and treated 8.25 % as 8.25 % available chlorine, you would have measured 12.12 mL instead of 12.73 mL, and your finished solution would have been about 4.75 percent weaker than intended — small, but in the wrong direction, and larger than the rounding on any of the other numbers.

strength BasissodiumHypochlorite
bleach Strength Percent8.25
final Volume Litres1
target Ppm1,000

Frequently asked questions.

Why is 8.25 % sodium hypochlorite not 8.25 % available chlorine?
Because they measure different things. Available chlorine is expressed as the equivalent mass of Cl₂ — the mass of elemental chlorine with the same oxidising capacity. One mole of NaOCl is equivalent to one mole of Cl₂, but NaOCl is the heavier molecule: 74.4388 g/mol against 70.90 g/mol, using the IUPAC/CIAAW standard atomic weights Cl 35.45, Na 22.98976928 and O 15.999. So a given mass of sodium hypochlorite carries only 70.90/74.4388 = 0.95246 times its own mass of available chlorine. Multiply any '% sodium hypochlorite' figure by 0.95246 before comparing it with a target in ppm available chlorine. The calculator does this for you when you select the sodium-hypochlorite basis.
What does a '1:10 dilution' actually mean?
It depends who wrote it, which is why this page prints both readings. In most laboratory and public-health usage, '1:10' means one part of stock in ten parts of finished solution — one part bleach plus nine parts water, a tenfold dilution. In some consumer and trade writing it means one part bleach to ten parts water, which is an elevenfold dilution. The two differ by ten percent. The calculator reports the dilution factor on the first convention (final volume divided by bleach volume) and the parts-of-water figure on the second, and spells both out in a sentence so there is nothing left to guess.
How many ppm is one percent?
Ten thousand. One percent weight-per-volume is 1 g per 100 mL, which is 10 g per litre, which is 10 000 mg per litre, and in a dilute aqueous solution one mg/L is one ppm by mass. So 0.1 % is 1000 ppm, 0.5 % is 5000 ppm, and household bleach at roughly 8 % available chlorine is roughly 80 000 ppm. Guidance documents quote the same concentration both ways, which is a common source of hundred-fold errors — if a calculation comes out a hundred times off, check whether a percentage has been entered where ppm was expected.
Does this page tell me what concentration to use?
No, deliberately. Chlorine-based disinfectants sold in the United States are registered pesticides, and 40 CFR §156.10(i)(2)(ii) requires every registered label to carry the statement 'It is a violation of Federal law to use this product in a manner inconsistent with its labeling.' The concentration, the contact time, the surfaces a product is approved for and any required rinse are all on that label, and they differ between products and between countries. Take your target from the label or from your local public-health authority, and use this calculator only to get from that target to a measured volume.
Why is my old bottle weaker than the label says?
Because sodium hypochlorite decomposes on standing, and faster when it is warm or exposed to light. The percentage printed on a bottle is its strength at manufacture, not today. An unopened bottle stored cool and dark loses strength slowly over months; one that has been open, warm, or on a sunlit shelf can lose a substantial fraction. The calculator has no way to know this, so it uses the number you enter at face value. If the concentration matters, verify the mixed solution with chlorine test strips rather than trusting the arithmetic alone.
What does this calculator not account for?
Quite a lot, and all of it deliberately. It does not model hypochlorite decay in storage. It does not model the pH-dependent equilibrium between hypochlorous acid and hypochlorite ion, which is what actually governs biocidal activity — the same available chlorine is far more effective at pH 6 than at pH 9. It does not account for chlorine demand, the fact that organic soil on a surface consumes free chlorine before any is left to act. And it says nothing about contact time, which matters as much as concentration. It is mixing arithmetic: it converts a label into a measured volume, accurately, and stops there. One safety point that is not arithmetic at all: never mix bleach with an acid or with an ammonia-containing cleaner.

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 'pressure' (P04819) and related quantity definitions establishing the amount-concentration and mass-concentration conventions used for the percent-to-ppm conversion (1 % w/v = 10 g/L = 10 000 mg/L = 10 000 ppm in dilute aqueous solution). Open access; retrieved 2026-07-29.
Related calculators
5
Dilution CalculatorcheMolarity CalculatorcheMolar Mass CalculatorchePartial Pressure Calculator (Dalton's Law)cheRaoult's Law Calculator (Vapour Pressure of Solutions)che

In this category

Embed

Quanta Pro

Paid features are coming later.

  • All 682 calculators remain free
  • No billing is enabled
Coming soon