If the distance between the tip of tongue and insertion of lingual frenum is 6 mm, then it will be:

Class 1 - Mild ankyloglossia - 12-15 mm Class 2 - Moderate ankyloglossia - 8-11 mm Class 3 - Severe ankyloglossia - 4-7 mm Class 4 - Complete ankyloglossia - 0-3 mm.