For Obtaining admissions how much should one score in class12

A minimum 75% aggregate marks in class 12th with all 5subjects appeared for geenral quota or  candidate can be in top 20 perentile to get admissions into top NITs, IIITs, GFTIs.

Although, criteria is relaxed to 65% marks for SC/ST category.

If any candidate appears for improvement exam, he can give either 1 subject or more than 1(less than 5 subjects) to make his score more than 75% as per new updated rules for 2018.

Below mentioned link shall provide deatils on improvement exams and Top20 percentile parameters to get into top IIts.

https://engineering.careers360.com/articles/jee-advanced-eligibility-criteria

Hope it helps..!!

Assuming you are asking for Jee main so to get admission in NITs, IIITs, GFTIs you will have to get either 75% or you should be there in top 20 percentile. Also, to get the complete information about its eligibility criteria you can go through the below link -

Jee Main Eligibility 2018

Hope this helps!!!