Hydrogen Peroxide Dilution Calculator
Use this hydrogen peroxide dilution calculator to dilute concentrated H₂O₂ (35% food-grade, 12% or 6%) down to 3% or any target strength. Enter your stock %, the % you want, and the final volume — it returns the peroxide and water to measure.
Enter your stock %, the % you want, and the final volume to get the peroxide and water to measure.
How to dilute hydrogen peroxide
Because diluting only adds water and keeps the amount of peroxide the same, the dilution equation applies:
C₁ is the stock strength (e.g. 35%), C₂ is the strength you want (e.g. 3%), and V₂ is the final volume. Solve for the stock volume:
The water to add is V₂ − V₁. Safety first: wear gloves and eye protection with concentrated peroxide, work in a ventilated space, and add H₂O₂ to the water, never water to concentrated peroxide.
Worked example
You have 35% H₂O₂ and want 500 mL of 3%. Set C₁ = 35, C₂ = 3, V₂ = 500: V₁ = (3 × 500) ÷ 35 ≈ 42.9 mL of 35% stock, plus 457.1 mL of water.
Common H₂O₂ strengths and what they're diluted for
"3%" and "35%" aren't arbitrary — they're what's actually sold on shelves, and each has a typical target concentration:
| Stock strength | Usually sold as | Common use | Typical target |
|---|---|---|---|
| 3% | Drugstore brown bottle | Household disinfecting, minor cuts | Use as-is — already the target strength |
| 6% (20 vol) | Hair developer | Bleaching, oxidative color | Rarely diluted further; some colorists cut to 4–4.5% (~13 vol) |
| 12% (35–40 vol) | Food-grade concentrate | Hydroponics, garden/soil drench | 0.3–1% for foliar spray, up to 3% for soil soak |
| 35% | Food-grade industrial | Bulk source for the above, teeth-whitening bases | Always diluted before contact — never used at full strength |
Related tools
For any solution rather than peroxide, use the home dilution calculator, or the dilution ratio calculator if you prefer working from a 1:N ratio.
Frequently asked questions
›How do I dilute 35% hydrogen peroxide to 3%?
Use the dilution equation C₁V₁ = C₂V₂. To make 100 mL of 3% from 35% stock: V₁ = (3 × 100) ÷ 35 ≈ 8.6 mL of 35% H₂O₂, topped up with about 91.4 mL of water. Always add peroxide to water, not the other way round.
›What is the formula to dilute hydrogen peroxide?
It is the standard dilution formula solved for stock volume: V₁ = (C₂ × V₂) ÷ C₁, where C₁ is your stock strength (e.g. 35%), C₂ is the target strength (e.g. 3%), and V₂ is the final volume you want. The water to add is V₂ − V₁.
›Is diluted hydrogen peroxide still effective?
Yes — 3% is the common household strength and works fine for cleaning and general disinfection. Diluting concentrated H₂O₂ just changes the concentration; the peroxide itself is unchanged. Store the diluted solution in an opaque bottle away from light.
›Is this hydrogen peroxide dilution calculator free?
Yes. It runs entirely in your browser, needs no sign-up, and never sends your values to a server.
›Why does the label say "volume" instead of percent (e.g. 20 volume)?
Hair developers are often sold in "volume" instead of %. Volume is roughly % × 3.3, so 20 volume ≈ 6%, 30 volume ≈ 9%, and 40 volume ≈ 12%. Convert to % first, then use this calculator as normal.
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