HI,

well it depends on the IIT you are going to, and the branch that you are trying for, and the category you are from.

Basically this depends upon ranking and cutoff for the session instead of marks, higher the difficulty level of paper-lesser the marks required to make good ranking.But in general, to get into IITs, the normal cutoff is around 650-700 GATE score (could be a bit higher too sometimes). To get such a score, you may have to have atleast 55-60 out of 100.

I will talk about general category.

Mechanical has 3 main branches . design, thermal and manufacturing.

as far as i know in every IIT design seats will get filled first, then thermal then manufacturing. (it may not be same every time)

at Madras you should get below 350 or 400 to get design (yeah! you will get it in last round if you are close to 350 or 400) and below 600 to get thermal and below 900 to get manufacturing.

and Kharagpur stands next to IIT madras. if you are below 600 you can expect design, for below 1000 and 1200 you will get thermal and manufacturing.

the information i gave is just for reference and the statistics may not be the same every year but they will be almost similar.

hope this answers your question.

any further query FEEL FREE to  comment .

ALL THE BEST