Hair Developer Calculator
Enter the amount of colour or bleach and the mixing ratio printed in the product's instructions. The calculator gives the amount of developer to add and the total mixture, and converts between grams and ounces or millilitres and fluid ounces. It does not choose a ratio or a developer strength for you.
Free, no sign-up. What you enter stays in your browser: it is not saved or sent to HerFound. Reviewed .
Measure in
Mixing ratio in the instructions (colour : developer)
The tube, sachet or scoop size is printed on the pack.
Enter the amount of colour or bleach to see how much developer to add.
Developer strengths, for reference
Developer is sold by volume. This table shows what each number means. It is not a recommendation: use the strength named in the instructions for your colour or bleach.
| Developer | Hydrogen peroxide |
|---|---|
| 10 volume | 3% |
| 20 volume | 6% |
| 30 volume | 9% |
| 40 volume | 12% |
Before you mix
- Follow the instructions in the box, including the ratio, the developer strength and the time. Do not leave the mix on for longer than they say.
- Do an allergy patch test 48 hours before every application, the way the instructions describe. Do not use the product if you react or feel unwell after the test.
- Never use hair dye or bleach on eyebrows or eyelashes, and keep it away from your eyes.
- Use only the developer that the instructions name. Do not mix products from different brands or ranges.
- Wear gloves and work in a room with fresh air, for example with a window open.
- Do not colour or bleach if your scalp is broken, irritated, sunburned or damaged.
- If your skin stings or burns, rinse the product off straight away with water and a mild shampoo.
Call 999, 911 or your local emergency number if your lips, mouth, tongue or throat swell, or you struggle to breathe or swallow. See a doctor or pharmacist if a rash, burning or blisters get worse or spread. Symptoms can take up to 72 hours to appear.
This is general information, not medical advice. It cannot take your own health history into account. For anything that worries you, speak to a doctor, midwife or pharmacist.
How it works
A mixing ratio is written as colour to developer. The sum is: developer = amount of colour or bleach x the developer part of the ratio. Total mixture = colour + developer. At 1:1.5, 60 g of colour needs 60 x 1.5 = 90 g of developer, which makes 150 g. At 1:2 it needs 120 g and at 1:3 it needs 180 g.
The answer is in the unit you entered. Weight converts to weight (1 oz = 28.35 g) and volume converts to volume (1 US fl oz = 29.57 ml). The calculator does not turn grams into millilitres, because creams and powders do not weigh 1 g per ml. Measure by weight or by volume, whichever the instructions use, and measure both parts the same way.
Developer strength is a separate thing from the ratio. It is sold by volume: 10, 20, 30 and 40 volume developers contain 3%, 6%, 9% and 12% hydrogen peroxide. The table under the calculator lists these as a reference only. Both the ratio and the strength come from the instructions for the exact colour or bleach you are using.
What it cannot tell you
- The calculator only does the arithmetic. It cannot tell you which ratio, which developer strength or how long to leave a product on. Those come from the instructions in the box, and they differ between products.
- It cannot make hair colour safe for you. Hair dye can cause allergic reactions, sometimes serious ones. Do an allergy test 48 hours before every application, as the instructions describe, even if you have used the product before.
- Call 999, 911 or your local emergency number if your lips, mouth, tongue or throat swell, or you struggle to breathe or swallow. See a doctor or pharmacist for a rash, burning or blisters that get worse or spread.
- It does not cover lash or brow tints. Do not use hair dye on eyebrows or eyelashes: the US FDA warns that this can hurt your eyes and may even cause blindness.
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Common questions
The amount of developer to mix with hair dye is the amount of colour multiplied by the developer part of the ratio on the box. At 1:1 you use the same amount of each. At 1:1.5, 60 g of colour needs 90 g of developer, and at 1:2 it needs 120 g.
A 1:2 mixing ratio means one part colour or bleach to two parts developer. For 30 g of product you add 60 g of developer and get 90 g of mixture. Measure both parts the same way, by weight or by volume, as the instructions say.
20 volume developer is 6% hydrogen peroxide. 10 volume is 3%, 30 volume is 9% and 40 volume is 12%. The strength to use is set by the instructions for your colour or bleach, not by this calculator.
Yes, do a patch test every time you dye your hair, even with a product you have used before. The US FDA says to patch test on your skin every time, and the NHS says to test at least 48 hours before use and to follow the instructions on the packet. Do not use the dye if you react or feel unwell after the test.
No, do not use hair dye on your eyebrows or eyelashes. The US FDA warns that this can hurt your eyes and may even cause blindness. Keep hair dye and developer away from your eyes.