You can calculate your rank using this formula :-

Rank=(total number of students -(percentile*0.01*number of students))

The total number of students that appeared in JEE MAINS 2019 were 9.65 lakhs. Hope this helps you. If you still have any other query. Feel free to ask.

It is difficult to predict the actual rank or JEE Advance qualifying marks as first time JEE is being conducted twice and rank will be based on NTA percentile score but you may calculate  your expected rank by given below Formula.

874469 are the number of candidates appeared for the January exam. So rank formula is (100- your total score) * 874469 / 100.

If the number of candidates for April exam increased to 1400000 then your final rank shall be (100- your total score) * 1400000/100.

Good Luck!