In order to be eligible for BITSAT 2018 you have to fulfill below eligibility criteria

-  You should have secured at least 75% aggregate marks in the qualifying examination with Physics, Chemistry and Mathematics.

-  Apart from the 75% aggregate marks, you should have scored 60% marks separately in each of the three subjects.

To check the complete eligibility criteria you acn refer below link

BITSAT Eligibility Criteria 2018

Good Luck!!