see bitsat exam is only for admission in bits pilani and associate campuses. so if you want to study engineering or pharmacy or m.sc courses in bits then you have to appear in bitsat exam. you may follow the below link to know about bitsat cutoff:
bitsat exam score is not evaluated by nits or iits. nits take admission based on jee main score, while iits admission is based on jee advance score. you have to secure a minimum score in jee main to become eligible to appear in jee advance test.
you may follow the below link to check jee main cutoff: