Hair Color Mixing Calculator

Introduction to weight-based hair colour mixing

Mixing hair colour is a ratio problem, and the reason it goes wrong at home is almost never the ratio itself. It is that the two questions people actually have — "how much developer do I add to this?" and "how much of everything do I need for my hair?" — are inverses of each other, and most calculators only answer the first. This one answers both: give it your colour amounts and it returns the developer, or tell it how much finished product you need and it works backwards to the colour and developer that add up to it.

The second thing worth being blunt about is measurement. Mix by weight, in grams, on a scale. Colour cream and developer have different densities, so a tablespoon of one is not the mass equivalent of a tablespoon of the other, and every manufacturer's ratio is specified by weight. A kitchen scale that reads to 1 g costs less than a single box of colour and is the difference between a formula you can repeat and one you cannot.

Everything below is arithmetic, not colour theory. The calculator cannot tell you what shade you will end up with, because that depends on your starting level, your hair's history and porosity, and the pigment in the tube. What it can do is make the bowl reproducible.

How to use the hair colour mixing calculator

1. Choose which direction you are solving. "I know my colour amounts" is the classic case: weigh the cream, get the developer. "I know how much total mixture I need" is the one you want when you are estimating for a whole head, and it splits the target back into colour and developer for you.
2. Pick the developer volume. This does not change the arithmetic; it changes the sanity check. The calculator knows the ratio bands that are usual for each volume and will tell you when the ratio you typed sits outside the band your product line normally uses, which is a prompt to re-read the box rather than an instruction.
3. Enter the developer ratio as parts per one part colour. Type 1 for 1:1, 1.5 for 1:1.5, 2 for 1:2. If your instructions say "mix 1 part colour with 2 parts developer", the number you want is 2.
4. Use the hair-length presets when working backwards. They fill the target with the mid-point of the usual range for that length, which you should then adjust for density — fine hair at the low end, thick or very long hair well above it.
5. Read the ounce column if your scale is imperial. Every figure is given in grams and in avoirdupois ounces at 28.3495 g per ounce.

The mixing formula, and its inverse

With and the two colour weights in grams and the parts of developer per part of colour, the forward direction is two multiplications:

That last form is the useful one, because it inverts cleanly. If you know the finished weight you want in the bowl, the colour you need is the target divided by one plus the ratio:

The fraction is worth internalising: at 1:1 developer is half the bowl, at 1:1.5 it is 60%, and at 1:2 it is two-thirds. When someone says a 1:2 mix is "mostly developer", that is the number they mean.

Splitting the colour across two shades is a proportion of the colour total, not of the whole mixture:

Plain-text formula: developerGrams = (color1Grams + color2Grams) * developerRatio; totalMixGrams = color1Grams + color2Grams + developerGrams; and inverted, colorGrams = targetTotalGrams / (1 + developerRatio).

Worked example: forwards and backwards on the same formula

Forwards. A custom brunette from 30 g of a neutral brown and 10 g of a warm red-brown, at 1:1.5.

1. Total colour = 30 + 10 = 40 g.
2. Developer = 40 × 1.5 = 60 g.
3. Total mixture = 40 + 60 = 100 g, of which developer is 60%.
4. In ounces: 1.41 oz colour, 2.12 oz developer, 3.53 oz total.

Backwards. Now suppose you have shoulder-length hair and want 90 g in the bowl at the same 1:1.5 ratio, keeping the same three-to-one shade split.

1. Total colour = 90 ÷ (1 + 1.5) = 90 ÷ 2.5 = 36 g.
2. Developer = 90 − 36 = 54 g.
3. Split 75/25: 27 g of the neutral brown and 9 g of the red-brown.

Note what did not change: the ratio, and therefore the colour result. Scaling a formula up or down is safe as long as the ratio is held; it is changing the ratio that changes the outcome, which is why "just add a bit more developer because it looks thick" is the single most common way a repeatable formula stops being repeatable.

Developer volumes and the ratios that go with them

The volume of a developer is its hydrogen peroxide strength and it decides how much the formula lifts; the ratio decides how much liquid is in the bowl. They are independent settings that people routinely conflate. Always check your product instructions first, but this is the usual pairing:

The calculator compares the ratio you enter against these bands and flags a mismatch. A flag is not an error — plenty of individual lines break these conventions — but it is a reason to check the tube before you commit a whole head to it.

How much total mixture a head of hair takes

• Short hair, above the ears, or a root-only retouch: about 30–50 g of total mixture.
• Medium hair, around the shoulders: about 50–80 g.
• Long or very thick hair, below the shoulders: about 80–120 g, sometimes more.

These are starting points, not rules, and density matters as much as length: fine long hair can take less than thick shoulder-length hair. Mixing slightly more than you think you need is the safer error, because running out mid-application leaves a visible line — but stay inside whatever the manufacturer allows for a single service.

Limitations, assumptions and safety notes

This is a weight-ratio helper, not a hair consultation, and it cannot predict your colour result.

• Brand-specific directions always come first. Different brands, and different lines within one brand, use different ratios and dedicated developers. The instructions on the box override every band shown here.
• Nothing here knows your hair history. Previous colour, bleach, henna, metallic dyes, relaxers and overall damage change both the result and the safety of a formula, and none of them are inputs.
• The gram targets by length are approximate. Density, porosity and strand thickness all move the real requirement, in both directions.
• Do not exceed safe developer volumes. Never use a higher volume than your product allows, and do not extend processing beyond the stated range. Volume and ratio are separate decisions; raising the ratio does not make a high-volume developer safer.
• Do not mix incompatible products. Avoid combining colour and developer from different brands unless the instructions explicitly permit it.
• Patch and strand tests are essential. Do a skin sensitivity test and a strand test before every new product or formula, not just the first one.
• Wear gloves and ventilate. Protect eyes and skin from splashes and mix in a well-ventilated space, per the product label.

For a significant lightening, a colour correction, or work on compromised hair, see a professional. This calculator is an educational tool for the mixing arithmetic. It is not a substitute for professional training, personalised advice, or the safety instructions supplied with your products.

Questions about mixing hair colour by weight

Sources and status of these figures. The developer volume table and the total-mixture ranges by hair length are standard salon conventions, widely published across professional colour education, rather than figures from a single authority; individual brands publish their own ratios and those always take precedence over anything here. The unit conversion uses the exact avoirdupois ounce of 28.3495231 grams. The arithmetic itself is exact: the forward relation is total mixture equals colour times one plus the ratio, and the reverse divides the target by one plus the ratio. This page is an educational mixing aid, not a substitute for the instructions supplied with your product or for professional advice, and it neither stores nor transmits anything you enter. Last reviewed 2026.