Vishnu, you haven't mentioned the exam you are enquiring about. But, in general, 90 percentile means you should have scored better than 90 percent of the Candidates who appeared for the exam. So to calculate 90 percentile, we will need the exam you are enquiring about and a rough estimate of Candidates who appeared for the exam. Even if you do not have an idea about the no.of people who appeared for the exam, please help us with the exam you are enquiring about and we shall help you with relevant information.