The Best How Much Developer Do You Mix With Hair Color References. Web traditionally, when combining hair dye and developer, the proportion should be 1:1. The importance of mixing hair dye and developer.
The higher the number, the more peroxide it contains, and the stronger its effect on your hair. Prepare both boxes together at the same time. So 10 would have the slightest lift, and 40 will open your hair cuticles up the most, making it the most damaging of the four.
