Hi

As in your case, your 12th Board has given you grade points instead of marks, you check whether you stand within the top 20 percentile of your respective 12th Board Examination or not.

To be eligible for any of the NITs or for JoSAA Counselling admission process, you have to secure atleast 75% of the total marks in 12th Board Examination ( 65% for SC/ST/PwD Candidates ) or Equivalent Examination. Otherwise, you have to secure a position within the top 20 percentile of your respective 12th Board Examination or Equivalent Examination.

You can always check the same about JEE Main Eligibility Criteria in a greater detail through this link: https://engineering.careers360.com/articles/jee-main-eligibility-criteria.

Best of Luck. 

Hope this helps.

Cheers!