Hair colour · Mixing
Hair dye developer ratio calculator.
Pick your ratio and how much colour (or total mix) you have. You get grams of colour and developer, and a second section shows how to weaken a stronger developer with water. Nothing you enter leaves your browser.
1. Mix colour and developer
2. Weaken developer with water (optional)
3. How much colour do I need?
Result
Check your product’s label for the right ratio and strength. Do a patch test and a strand test before colouring.
How the mixing and dilution maths works
Mixing by ratio
A ratio of 1:x is 1 part colour to x parts developer. The total is 1 + x parts. If you know the colour weight c, developer = c × x and total = c × (1 + x). If you know the total T, colour = T ÷ (1 + x) and developer = T − colour. Example: 1:1.5 with 40 g of colour is 40 × 1.5 = 60 g of developer, 100 g in all. Figures are rounded to 0.1 g. Developer is mostly water, so its millilitres are close to its grams; colour cream is thicker, so use grams for it.
Volume strength and percent
“Volume” describes how much oxygen a developer can release. Hydrogen peroxide breaks down as 2 H2O2 → 2 H2O + O2. One litre of oxygen gas at 0 °C and 1 atm is 1 ÷ 22.414 mol, and it takes twice that many moles of peroxide to make it: 2 ÷ 22.414 × 34.015 g/mol = 3.035 g. So 1 volume is about 3.04 g of H2O2 per litre, or about 0.30% when the solution is treated as 1 g/mL. We use 0.3035% per volume, and treat percent as weight in weight.
| Volume | Exact % H2O2 | Usually quoted as |
|---|---|---|
| 10 vol | 3.04% | about 3% |
| 20 vol | 6.07% | about 6% |
| 30 vol | 9.11% | about 9% |
| 40 vol | 12.14% | about 12% |
The rounded figures come from rounding the exact ones to the nearest whole percent. Your bottle may state its own percent; if it does, trust the bottle.
Diluting with water
Adding water to developer keeps the amount of peroxide the same and spreads it over more mass, so strength × mass stays constant: C1V1 = C2V2. To end with T grams at target strength C2 from stock strength C1, you need T × C2 ÷ C1 grams of stock and the rest in water. Because volume strength is proportional to percent, you can use volumes directly: 20 from 30 is 20/30 = 2/3 developer and 1/3 water. Example: 60 g of 20 volume from 30 volume is 40 g developer and 20 g water. Water only lowers strength; it cannot raise it.
Practical caution: commercial developers also contain stabilisers and are pH adjusted. Diluting with water dilutes those too, and some manufacturers tell you not to. This page does the sums. It does not say your product can be diluted.
Limits of this tool
- It does arithmetic only. It does not know your product, your hair history or your skin.
- It does not tell you which developer strength or ratio gives which result. Use the instructions that came with your colour.
- Hydrogen peroxide in hair products is regulated, and Health Canada’s Cosmetic Ingredient Hotlist lists it as a restricted ingredient. This tool does not check any mix against a legal limit. Check the Hotlist and your product label for current rules.
- The “how much do I need” presets are our own rough defaults, not measured facts.
Sources
- PubChem, Hydrogen Peroxide (CID 784): molar mass 34.015 g/mol; decomposition to water and oxygen.
- NIST CODATA, molar volume of an ideal gas at 273.15 K and 101.325 kPa: 22.414 L/mol, used for the volume-to-percent derivation. The volume figures here are our own derivation from these two values, rounded as stated above.
- Health Canada, Cosmetic Ingredient Hotlist: hydrogen peroxide appears among restricted ingredients. No limit is quoted on this page.
Cite this page: TNAADO Tools, “Hair Dye Developer Mixing Calculator,” tools.tnaado.ca/calculators/general/hair-developer-mixing-calculator/, constants checked October 1, 2026.
Hair developer ratio FAQ
What does 1:1.5 mean for hair dye and developer?
It means 1 part colour to 1.5 parts developer, by weight or by volume as long as you use the same measure for both. 40 g of colour needs 60 g of developer, which makes 100 g of mix. Weighing on a small kitchen scale is more accurate than measuring cups.
Which ratio should I use?
The one printed on your colour’s label or instructions. Different products are formulated for different ratios, and this calculator only does the arithmetic. It cannot tell you which ratio your product needs.
What do 10, 20, 30 and 40 volume mean?
Volume is how much oxygen gas one volume of the developer can release as the peroxide breaks down. One volume is about 0.30% hydrogen peroxide, so 10, 20, 30 and 40 volume are about 3%, 6%, 9% and 12%. The exact figures are 3.04%, 6.07%, 9.11% and 12.14%; manufacturers round them.
Can I turn 30 or 40 volume developer into 20 volume with water?
Arithmetically yes: 20 volume from 30 volume is 2 parts developer to 1 part water, and from 40 volume it is 1 part developer to 1 part water. This page shows the amounts. But water also dilutes the stabilisers and pH buffers in the developer, and many manufacturers say not to do it. If a product tells you to use a specific developer, use that. If you want a weaker developer, buying the weaker bottle is the safer route.
Do I mix by weight or by volume?
Either works if you use the same one for both. Developer is mostly water, so 1 gram is close to 1 mL. Colour cream is thicker and its density is not stated on most labels, so grams are the more reliable choice.
How much dye do I need for my hair?
It depends on length, thickness and whether you are doing roots or the whole head. The estimator on this page starts from rough, editable guesses, not facts. Mix a little more than you think you need, because a second batch mixed later will not match the first as it ages.
Do I need a strand test or patch test?
Yes. Always follow your product’s label ratio and do a patch test and a strand test before colouring. This page does not replace the instructions that came with your product.
Read this first
This calculator does arithmetic on the numbers you enter. It does not know your product. Follow your product’s label ratio and instructions, and do a patch test and a strand test before every colour. Do not mix products or dilute developer unless the manufacturer says it is fine.