Hello 

JEE mains is only for the admission in NIT / IIIT /GFTI s .

After qualifying JEE mains you have to give JEE advanced and both have their separate rank list and JEE advanced rank will decide your admission in IIT s

And you have to secure rank under 7-8 thousand to get admitted in IIT ( rank may vary according to specific college and branch).

And to qualify JEE mains you have to secure minimum 85-90 percentile score.( May vary ).

So good luck.