Hello Deepanshu, 

Let me tell you one thing, it is not constant always as level changes frequently. A lot of variations are there every year. The Cut-off basically depends on the paper whether it's tough or easy to score and also depends on your rank and the rank depends on level of paper and number of students appeared in the examination. 

I am listing the cut-off(Branch-wise) for the last year, 2018 :

• Civil : Opening-180 Closing-2012
• Chemical : Opening-1497 Closing-2659
• Computer Science and Engineering : Opening-58 Closing-508
• Electrical Engineering : Opening-683 Closing-1416
• Electronics and Communication Engineering : Opening-379 Closing-1219
• Electronics and Instrumentation Engineering : Opening-1419 Closing-2179
• Information Technology : Opening-516 Closing-980
• Mechanical Engineering : Opening-557 Closing-1344

Above mentioned ranks are of general category. So, now you can judge your rank as paper difficulty of 2018 was quite similar to 2017. Just keep one thing in your mind, you must try to score atleast 450 marks (under 3000 rank)to deserve some core branches in IET Lucknow.

Hope it helps you!!

All the best :)