The format is described as 50 ml colour cream, 50 ml developer and an additional 30 ml portion. The colour cream and developer are mixed for oxidative colouring; once mixed, the formula starts to react, so it should be applied immediately according to the enclosed instructions and not stored for later use.
If you are colouring virgin hair or changing the overall depth, the mixture is usually applied through the hair so the roots, mid-lengths and ends are evenly covered. If you are maintaining an existing brown shade, you may need more precision: apply first to the regrowth, where the natural hair or grey is visible, then refresh the lengths only as the instructions advise. This helps avoid unnecessarily building up colour on already-coloured ends.
Hair length, thickness and porosity affect how much mixture is needed. Thick, long or very absorbent hair requires more product to fully coat each section; patchy saturation can lead to uneven results. Work in small sections, use gloves, protect clothing and wipe accidental skin staining promptly. Do not use the product on eyelashes or eyebrows, and avoid application if the scalp is irritated.