There is no single uniform, standardised, and reproducible grading system for severity of acne. Acne is commonly classified by type (comedonal/papular, pustular/nodulocystic) and/or severity (mild/moderate/moderately severe/very severe). Skin lesions can be described as inflammatory or non-inflammatory.
Leeds technique 
Assessment of severity, used primarily for research, using grades 1 to 12 (mild to severe).