My PNT is:
8" Deep
14" Wide
22" Tall
Depth & width are the key for the CRJ overhead, anything more than 8x14 won't work.
It can be as long as you want...22" exceeds legal carry-on size, but they don't enforce that for crews anyway. The 22" will barely fit wheels first in a Boeing bin, so that's handy. In the RJ (and many MD bins) it has to go sideways.