What is cut off Marks ?  
Cut off marks is the mark to rank the score. The subjects Physics, Chemistry and Maths will be considered for calculating cutoff marks. Based on your cut off mark rank list will be prepared for admission.
Why cut off mark is important  
Cut off mark is very important to get admission in colleges. Your cut off mark will be considered to attend counselling and not your whole mark in 12th standard. 
How to calculate cut off mark for Anna University Counselling  
To calculate 12th cut off marks for anna university counselling for Engineering BE/B.Tech take 3 subject marks(Physics, Chemistry, Maths)       
Subjects Total Marks Cut-off Calculation Cut-Off Marks
Mathematics 200 200/2 100
Physics 200 200/4 50
Chemistry 200 200/4 50