Household chlorine bleach is a water solution of sodium hypochlorite (NaOCl), usually 5–8.25% on the label in North America and 3–5% in many other countries. Used straight it is far stronger than needed and damages surfaces and skin, so it is always diluted to a target concentration expressed in parts per million (ppm, equal to mg per litre). Typical targets are about 50–200 ppm for sanitising food-contact surfaces and dishes, around 1,000 ppm for general disinfection, and around 5,000 ppm for heavy contamination.
The arithmetic is a dilution: the mass of hypochlorite in the bleach you measure out must equal the mass in the finished solution. Because the label percentage is by mass, a precise answer uses the bleach density (about 1.07–1.12 g/mL); many guidelines simply treat the percentage as grams per 100 mL, which is within about 10%. You can also express the target as “available chlorine” (the Cl₂ equivalent used by some standards), which is 0.952 times the NaOCl figure.
Always add bleach to cold water, never mix bleach with ammonia, vinegar or other cleaners, and make a fresh solution daily because hypochlorite slowly decomposes.
How to use the Bleach Dilution Calculator
- Bleach strength on the label (sodium hypochlorite)
- How to read the percentage
- Bleach density — About 1.07–1.12 g/mL for household bleach; check the safety data sheet.
- Target is expressed as
- Target concentration
- Amount of diluted solution to make
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
The calculator multiplies the target concentration by the final volume to get the milligrams of hypochlorite needed, divides by the hypochlorite content of the bleach (percent × density) to get the bleach volume, and subtracts that from the final volume to give the water to add and the dilution ratio.
Worked example
Make 1 US gallon (3.785 L) of 1,000 ppm disinfecting solution from 6% bleach (simple reading). Hypochlorite needed = 1,000 mg/L × 3.785 L = 3,785 mg. The bleach holds 6 g per 100 mL = 60,000 mg/L, so the bleach volume = 3,785 / 60,000 = 0.0631 L = 63.1 mL, about 4¼ tablespoons. Add it to 3.72 L of water; the ratio is about 1 : 59.
With the exact reading (density 1.08 g/mL) the bleach holds 64,800 mg/L and you need 58.4 mL instead.
Strength of common household recipes (6% bleach, simple reading)
| Recipe | Approximate strength |
|---|---|
| 1/8 tsp per US gallon | ≈ 10 ppm (emergency drinking water) |
| 1 tbsp per US gallon | ≈ 233 ppm (sanitising) |
| 1/3 cup per US gallon | ≈ 1,220 ppm (disinfecting) |
| 4 tsp per US quart | ≈ 1,220 ppm (disinfecting) |
| 1 part bleach + 9 parts water (1:9) | 6,000 ppm (heavy contamination) |
Tips
- Use the final volume of the solution, not the volume of solvent added, for molarity.
- For dilutions, C₁V₁ = C₂V₂ only holds when both concentrations use the same unit.
- Add acid to water, never water to acid.
- Everything is calculated in your browser.
Common mistakes to avoid
- Mixing w/w, w/v and v/v percentages.
- Forgetting that pH is logarithmic – one unit is a tenfold change in [H⁺].
- Using pKa where Ka is asked for (or the other way round).
Inputs explained
| Field | What to enter |
|---|---|
| Bleach strength on the label (sodium hypochlorite) | In % |
| How to read the percentage | Choose one: Simple: % = grams per 100 mL (common guidance), Exact: % by mass, use the bleach density |
| Bleach density | Units: g/mL, g/cm³, kg/m³, kg/L, lb/ft³. About 1.07–1.12 g/mL for household bleach; check the safety data sheet. |
| Target is expressed as | Choose one: ppm of sodium hypochlorite, ppm of available chlorine (Cl₂) |
| Target concentration | Units: ppm (mg/L), % (g/100 mL), g/L |
| Amount of diluted solution to make | Units: L, mL, US gal, qt (US), cup (US), fl oz (US) … |
What each result means
- Bleach to add = [Hypochlorite needed]÷[Hypochlorite in the bleach]
- Water to add = [Amount of diluted solution to make] – [Bleach to add]
- Dilution ratio (parts water per 1 part bleach) = [Amount of diluted solution to make]÷[Bleach to add] – 1
- Final strength as available chlorine = [Hypochlorite needed]÷[Amount of diluted solution to make]×70.906÷74.442
Formula
Mass of NaOCl needed (mg) = target (mg/L) × final volume (L) · Bleach volume = mass ÷ (bleach % ÷ 100 × density × 1,000 mg/g) · Ratio = 1 : (V_final ÷ V_bleach − 1)Worked example
Inputs — Bleach strength on the label (sodium hypochlorite): 6 %; How to read the percentage: Simple: % = grams per 100 mL (common guidance); Target is expressed as: ppm of sodium hypochlorite; Target concentration: 1,000 ppm (mg/L); Amount of diluted solution to make: 1 L.
Results — Hypochlorite needed = 1,000 mg NaOCl; Bleach to add = 16.6667 mL; Water to add = 0.9833 L; Dilution ratio (parts water per 1 part bleach) = 59; Final strength as available chlorine = 952 ppm; Use = Disinfecting strength (hard surfaces, bathrooms).
Key terms
- Sodium hypochlorite
- NaOCl, the active ingredient of chlorine bleach.
- ppm
- Parts per million; for water solutions 1 ppm ≈ 1 mg/L.
- Available chlorine
- Hypochlorite content expressed as an equivalent mass of chlorine gas, Cl₂.
- Dilution ratio
- Parts of water added per part of bleach, written 1 : x.
Frequently asked questions
How much bleach per gallon of water for disinfecting?
Common guidance for 5.25–8.25% bleach is 5 tablespoons (1/3 cup) per gallon, or 4 teaspoons per quart. With 6% bleach that gives roughly 1,200 ppm sodium hypochlorite.
What does ppm mean for bleach?
Parts per million by mass, which for water solutions is the same as milligrams per litre. 1,000 ppm = 0.1% = 1 g per litre.
How much bleach to sanitise dishes?
About 1 tablespoon of 6% bleach per gallon of water gives roughly 230 ppm; many food-safety codes ask for 50–200 ppm with a contact time of at least one minute.
How do I disinfect drinking water with bleach in an emergency?
US EPA guidance for 6% unscented bleach is about 1/8 teaspoon (8 drops) per gallon of clear water, about 10 ppm, then wait 30 minutes. Use double for cloudy water.
Why does my bleach strength matter?
Concentrated (8.25%) bleach needs about 27% less product than 6% bleach for the same ppm; older bleach loses strength, so use a fresh bottle.
What is available chlorine?
The oxidising power expressed as the mass of Cl₂ it is equivalent to. One mole of NaOCl (74.44 g) equals one mole of Cl₂ (70.91 g), so available chlorine = 0.952 × NaOCl.
How long does diluted bleach last?
Diluted solutions lose strength within a day, faster in sunlight and warmth – mix a fresh batch each day.