Dear Akash,

you have to score minimum  40% to 50%  (range) of the total marks  to be an IITian.

After little bit search on the internet I found that comparison between marks and rank

Also I would like to tell you that this is tentative data of 2017.

So,here is the rank vs marks in jee advance 2017:-

1.120 marks: not qualified.

2.141 marks: 23k AIR

3.152 marks: 17111 AIR

4.159 marks: 16500 AIR

5.186 marks: 9200 AIR

6.234 marks: 2900 AIR

7.270 around: 600–700 AIR

I think now you can figure out that how much you required for your preferred branch and IIT.

here the link from where you can be able to compare your marks and rank for IIT Madras

https://engineering.careers360.com/articles/iit-madras-cut-off

copy this link and paste another tab then you can see your the rank of IIT Madras college.

hope it helps.