Hello , 

It changes from time to time depending on the topper's marks .

Also it depends which NIT you want , you can get NIT with marks 60–70 range and also with 170–180 marks.

To get admission in high ranked NITs you gotta score high marks irrespective of having category benefit like score marks( 200–225). For other NITs you can also get admission with score of (75–100).

Choose particular NIT you wish to go and choose branch , then target and try to score good marks leaving the thought you can get admission with low marks .