You have to score at least 170+, to get an NIT. Also it depends on the choice of your branch. I know everyone wants computer science, but for that your rank must be under 2500. And to get rank under 2500, score at least 240+ . But relax 170+ is optimum for any NIT if you are ok with mechanical, electrical and so on.

Sometimes it depends on Home state quota. Suppose your rank is 12000 in jee mains but you are from Rajasthan then it is too difficult for you to get NIT Jaipur through home state. But with same rank you are from Odisha then you easily get NIT Rourkela through home state.

Now let's talk about OBC category, if you are in OBC category then if you score 140+ you may easily get one of the top NIT. But you have to compromise with branch. If your OBC rank is within 1000 then may be you get CSE branch. Cut for OBC is varies from 50–70 marks. So, don't be so panic work hard and take the benifit of what you have.

At last if you are in SC/ST OR PHYSICALLY CHALLENGED then be relaxed and score just 60–70 marks and you can easily get NIT. But here also the seats are very less in number. So be careful with that. Take all the benefits that what you have, never thought about others. If you score at least 120+ marks then definitely you will get any NIT. Just close your eye and put your finger over any top NIT with any branch.