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

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