The best peroxide volume for coloring hair depends on the difference between the natural hair shade and the dye, but volumes between 20 and 40 are considered standard. For gray hair, volumes of 10 or less are used because the hair is more brittle.
The appropriate peroxide volume is based on the amount of "lift" or change that must occur to achieve the desired shade. If the dye is several shades lighter, for example, a greater volume of peroxide is required. For more subtle changes, lower volumes are appropriate. When peroxide is included as an ingredient in hair dye, the product is considered either permanent or semi-permanent. Dyes without peroxide wash out of the hair over a period of days or weeks.