Hair Dye Volume Calculator

Why getting the quantity right matters

Running out of hair dye mid-application is one of the most common home colouring mistakes. It results in uneven colour, patchy roots, and visible demarcation lines that are difficult to fix without professional help. Buy one box more than the figure below. The asymmetry is what makes this an easy call: mixed dye cannot be kept once the developer is in it, but an unopened box goes back to the shop or sits in the cupboard until next time.

Standard box contents

A standard box of home hair dye holds roughly 80 to 100 ml once the colour and the developer are mixed, and the calculator uses 100 ml unless you tell it otherwise. Semi-permanent and toning products often come in smaller tubes of 50 to 60 ml, so check the box and put the real number in. Getting that wrong is the second most common way people end up short.

Hair length and thickness guide

Hair length is measured from the roots to the tips:

• Short: above the ears or chin (up to ~15 cm / 6 inches)
• Medium: collar bone to shoulder length (approximately 20–35 cm / 8–14 inches)
• Long: mid-back to waist (35–65 cm / 14–26 inches)
• Very long: below waist (65+ cm / 26+ inches)

Hair thickness (density) describes how many individual strands you have, not the diameter of each strand:

• Fine/thin: you can see the scalp clearly; a ponytail is less than 2 cm across
• Medium: a ponytail is 2–4 cm across
• Thick/coarse: dense, heavy hair; a ponytail is over 4 cm across

Root touch-up vs full application

For a root touch-up only (2–3 cm of regrowth), you typically need 50% or less of the amount required for a full application. This calculator assumes a full, all-over colour application from roots to tips.