what is the total number of seats in all IIT's
Hello vasudev,
According to latest update total no seats in nit and iit are as follows :-
Seat in IIT are -11,169
Seat in NIT are-17,868
Total no seats in nit and iit are -29057 for 2018 counseling.
Total nearly 36k seats if included iiit, gfti along With nit and iit.
Recently Govt take an important decision to increase the percentage of girl in nit and iit.
for more details and seat matrix visit: https://josaa.nic.in/SeatInfo/root/SeatMatrix.aspx

You can check the below provided seat matrix of IITs below -
https://josaa.nic.in/SeatInfo/root/SeatMatrix.aspx
Good Luck!!!