What Your Percentage Grey Actually Changes
"How grey are you?" is the first question in any colour conversation, and the answer changes the product, the developer and the mixing ratio. It is also not the only input: hair texture overrides the percentage entirely in one direction.
What the percentage recommends
From the grey coverage calculator, on medium-length, medium-texture hair:
| Percent grey | Product type | Developer | Mix |
|---|---|---|---|
| 10% | demi-permanent | 10 vol | 2:1 blend — 2 parts natural-level shade to 1 part gray-coverage shade |
| 30% | demi-permanent | 10 vol | 1:1 blend — equal parts natural-level shade and gray-coverage shade |
| 50% | permanent | 20 vol | Full-strength target shade (no blend needed) |
| 75% | permanent | 20 vol | Full-strength target shade (no blend needed) |
| 100% | permanent | 20 vol | Full-strength target shade (no blend needed) |
The threshold sits at 50%. Below it a demi-permanent blend does the job: it deposits tone without lifting, fades gently rather than leaving a line, and is far less committing. At or above it, full permanent colour with 20 volume developer becomes the recommendation.
Coarse hair changes the answer at any percentage
At the same 20% grey, medium-texture hair gets 10 volume and a blend; coarse hair gets 20 volume and permanent colour, because coarse grey is resistant — the cuticle is tighter and the hair takes colour reluctantly.
That is the single most common reason a home colour "does not take" on the greys while working everywhere else. It is not the shade. It is that resistant hair needed a stronger developer and a longer processing time than the box assumed.
What developer volume actually does
Developer is hydrogen peroxide, and the volume number is its strength. From the developer calculator:
10 volume — deposit-only, no lift; refreshes tone or blends a few grays
20 volume — standard gray coverage, lifts natural hair roughly 1-2 levels while depositing full color
Higher volumes lift more, which sounds like more coverage and is the opposite. Lift opens the cuticle and removes natural pigment; coverage is about depositing new pigment into grey hair that has none. Going up a volume to "cover better" typically produces brassier, lighter results that cover no better at all.
Why grey behaves differently from pigmented hair
Grey hair is hair without melanin. There is nothing to lift, so lifting does nothing useful, and there is nothing for the new colour to sit alongside — so it shows the deposited pigment more purely than pigmented hair does.
That is why a shade looks brighter or flatter on grey than on the rest of the head, and why the blends at lower percentages mix a natural-level shade with the coverage shade: the natural level gives the deposit something to read against.
Getting a realistic percentage
Most people overestimate. Grey concentrates at the temples and the parting, which is exactly where you look, and the back of the head is usually far less grey than the front.
Look at the whole head, with a mirror behind you, in daylight.
Assess dry, unstyled hair. Product and heat both change how visible grey is.
Think in quarters rather than exact figures — the recommendation only changes at the 30% and 50% boundaries, so precision beyond that buys nothing.
Where this stops being a calculator question
Everything above is about chemistry and coverage. None of it decides the shade, which depends on skin tone, eye colour and what you want, and none of it can see your hair's condition — previously coloured, heat-damaged or chemically treated hair behaves differently from virgin hair at the same percentage.
Use the recommendation to know what class of product you need and what developer goes with it, then patch test. And if the answer keeps coming back permanent at 20 volume and you would rather not, the grow-out arithmetic is the other option, with its own quite different timeline.
How often the roots come back
This is the part of colouring that people underestimate. Grey roots become visible at a few millimetres, which at ordinary growth rates is a matter of weeks rather than months — so permanent coverage is a standing commitment rather than a single decision.
That cadence is what the root touch-up scheduler exists for, and it is worth looking at before committing to permanent colour. The chemistry question and the every-few-weeks question are really the same decision.
Coverage versus blending, stated plainly
Coverage makes grey hair the same colour as the rest. It is opaque, it is permanent, and it produces a hard line at the root as it grows.
Blending makes grey hair less noticeable without matching it. It is translucent, it fades rather than growing out in a line, and it asks far less of the schedule.
The percentage table pushes towards coverage above 50% for a reason — blending cannot do much when most of the head is grey — but below that threshold blending is frequently the better answer and is offered less often, because it is a smaller sale.
Before any of it, patch test
Permanent colour and higher-volume developers are the products that provoke reactions, and a reaction to hair dye is not a minor event. Patch test every time, including with a product you have used before, because sensitisation develops with exposure rather than arriving on first contact.
Nothing on this page is medical advice, and a calculator cannot see your scalp. If in any doubt, this is a conversation for a colourist or a doctor rather than a tool.
The short version
Under 50% grey on ordinary hair: a demi-permanent blend at 10 volume, mixed with a natural-level shade. At or above 50%, or on coarse hair at any percentage: permanent colour at 20 volume. Higher developer does not mean better coverage, and the roots come back on their own schedule regardless of which you choose.
Run your own figure through the coverage calculator with your real texture rather than the one you would prefer — coarse is the input that changes the answer most, and it is the one people most often get wrong about their own hair.