Hi there,
Hope you are doing well.
To know your marks from your percentile, you must have the data of marks vs ranks.
Since percentile can only be converted into rank and not marks.
 Your rank would be = ( 100 - percentile ) * ( no of students appeared / 100 )

Then you can check rank vs marks stats.
hope it would help.
Thank YOu

Hey !

You can not calculate your accurate percentile from your marks. But you can surely calculate your rank by using the given formulae:

Your percentile=(your rank /total no. Of candidates who appeared for the exam) × 100

If its taken for marks , then suppose your marks to be 50 , and no. Of students who scored less than 50 is 15000 and total no. Of students are 40000 then your percentile is (15000/40000)×100.

But an approximation of your marks can be taken using the formulae 

Your percentile=(your marks/marks obtained by topper)×100

Hope you get it!