Mains rank use to predict with 60% jee mains score and 40% 12 percentage. But now it is no more available.Now ranks are predicted only on the basis of score and 12 percentage marks are required for qualifying for NIT and IIT(which is 75%) but for others it is normal.So just ranks is taken in consideration for predicting your college.

Now colleges are given on main rank provided one score 75% in boards if he is general and obc and 65% for sc st

Most colleges(private and government) gives admission on the basis of jee mains rank(almost 90% colleges)....some of the colleges only gives admission through 12th boards percentage......or there are other entrance exams through which you can get Admission.....best of luck

Dear Yash
Almost 95% in all Indian engineering colleges are given by jee rank base and 4% includes both jee rank and 10+2 marks and only 1 percent colleges gives admission in the basis of 10+2 marks.
All the best.