Well according to last year as of 2017, for general category it was around 180s i.e (your boards percentage + half of your nata score) and to get into J.J you must score a minimum around 165 .

For eg: if your boards percentage are 90 then you need to score around 170 in nata so your main score would be 170/2 = 85 and 85+90= 175

That would be a decent score to get into J.J College.

Thank you.