How to know your rank and marks from percentile??

Vin,

There's no way to know the marks from percentile
Though you can calculate your rank from your percentile by using the formula

((100-percentile)*no of candidates who gave the exam) /100.

This is the formula you can use.

And there's no such way to calculate marks from percentile. You can just have a average figure like if some percentile is 98.6 his marks will be like 170-180.

To make this easier for yourself, you can visit the link below which is Careers360 rank predictor

https://engineering.careers360.com/jee-main-rank-predictor