Well, it depends on your branch preference and also which iits you consider as "good". Cutoffs are much higher in old IITs of Delhi, Kanpur and Bombay than the newly opened ones.
JEE Board offered ranks to students scoring above 123 marks in JEE '14 which went approximately to AIR 19000. However, General category students only upto AIR 9000 were considered for counselling and no student with AIR above 7500 got any branch in any IIT.
The cutoffs in JEE are increasing drastically every year - and there is no fixed cutoff. The maximum marks and type of paper is also unpredictable. To be on the safe side, you should aim to get at least 48% of maximum marks - which would give you a rank around 4500. However to get a descent branch at a " good" IIT, a rank at least below 3500 is a must.
I hope this helps :) Good luck.