I used to be able to do 30 until I herniated a couple disks in my back. How many can you do on a flat surface? Can you do pull ups on a door frame? I used to be able to do five or six on just my fingertips.
I can do 7 or 8. A little more if I've had a can of red bull.
How exactly am I supposed to do door frame pullups? Do you mean clench the top of the door frame with my whole hand or use both hands, vicelike?