Percentage in 12th class differs as per colleges and entrance exams. 

If you want to take admission in IITs/NITs/IIITs and GFTIs then you should have 75% marks in your boards exam or you should be in top 20 percentile. For ST/SC you should have 65% marks.

For DTU and NSIT you should have 60% aggregate marks in P/C/M. There is a relaxtion of marks for reserved category.

2- BITSAT-  In order to be eligible for this exam you should have 75% aggregate marks in Physics, Chemistry and Mathematics  in your 2th class. Also, in each of the 3 subjects, they must also secure 60% marks separately.

3- VITEEE- In order to be eligible for this exam you should have scored an aggregate of 60% in Maths, Physics and Chemistry in 10+2 and for SC, ST, J&K, North Eastern states you should have scored an average 50% marks in Physics, Maths and Chemistry in 10+2 or its equivalent exam.

To know about all the entrance exam you can refer below link

https://engineering.careers360.com/exams

Do you want to know about any specific college or exam?