Cutoff rank depends upon your branch and type of IIT .In order to get admission after btech through Gate results ,you require good rank under 800 for IITs and under 1000 for NITs.If you are from mechanical then this figure will change,domain of rank for mechanical is quite high as lot of participants participate in exam minimum rank required for admission is under 1500.For other branch this not happens ,for electrical minimum rank requires take admission in IITs is under 400-600and for NITs under 800.

To get call from psu you require rank under 500 and for mechanical branch this figure get changed ,you require under 1000.This may get changed as it depends upon vaccanvac and type of PSU 

I hope you will satisfied with my answer .Let me know if you have any queries ,feel free to ask query