Baitcaster reel size

[Admau1]

Hi all, can anyone throw any light on the size of Bait casting reels ? I find the sizes a little confusing. 100,150 200,300 ? Is this just an indication of line capacity ?or is there more to it than that ?. Is there any application differences between them ? i.e.,100 small lures,300 big lures ?
Thanks in advance !

[Mark_Houghton]

Generally, the smaller the number the smaller the reel, and the smaller (and lighter) the spool, the easier it will handle light lures