You can never tell definitely, how much marks you need minimum. It changes every year, and you can never tell because the marks are never constant. But the ranks are almost always pretty similar. So I'd say try to keep your marks above 160 in JEE MAINS, then if not those NITs, you'll get some NIT definitely. All the best!

Dear Raghav, the answer to this question is not absolute . It depends on a number of factors.

Normally,the cutoff score for qualifying for JEE Advanced is around 100/360 ( for general category students) and around 2 lakh students qualify . So,roughly speaking,a score of 100 gives you a rank of about 2 lakh.

It also depends on how high you are aiming.If you want to go for NITs situated in the north east,a score of about 130–140 will be enough but if you are eyeing top NITs like NIT Trichy, you better rock the show and get 270+.Also,the cutoffs for IISc are insane,and usually about 290+.

One more thing,there is a home state quota for the students of the particular state.Due to this reservation of seats,a student of home state has better prospects of getting a seat than an outsider.

All the best 

Hope this helps