Hello Akash .

Marks and cutoffs of JEE advanced changes every year. No one accurately tell you exactly what marks you should secure to get in IITs but yeah we can predict a approximate value after analysing the previous year data.

Branches like CSE, and electrical engineering have higher cutoff that is you must have a rank under 270 to get a seat in these branches . For mechanical a rank within 750 would work whereas for civil branch rank around 2000 can get you a seat in iit Bombay here is the rank vs marks in jee advance 2017:-

1. 152: 17111 AIR
2. 186 marks: 9200 AIR
3. 159 marks: 16500 AIR
4. 235 marks: 2616 AIR
5. 141: 23k AIR
6. 223: 3368 AIR
7. 120 marks: not qualified.
8. 143 marks: 22,610 AIR
9. 234 marks: 2900 AIR
10. 270 around: 600–700 AIR
11. 188 marks: 8800 AIR (approx)
12. 186: 9200 AIR

I think now u can figure out that how much u required for ur preferred branch and IIT.

Thanku I hope it helps