Dear candidate, for IIT MADRAS your rank should be less than 3.7k.  As per the previous year cut offs this rank fetched seat for GEN category in CIVIL ENGINEERING.

For SC it was 1.5K. Likewise for OBC and ST, it was 2.6k and 709 respectively.

Amy ranks below them would certainly create high chances of you to get seat in IIT MADRAS. Having said that cut offs change every year as they depend on various factors like number of students appeared, highest score, lowest score etc.

You can check this link for previous year cut offs

All the best

Hope this helps