monitor size & room size advice needed

[33tetragammon]

hi all,

how can you determine if a studio monitor is too big/small for your room.
how do you calculate or measure something like that?

my room is 3 x 4 x 2.2(W x L x H,meters),acoustically treated with acoustic foam and basstraps.
my current monitors are Mackie hr824,which are going to be replaced by either Genelec 8020 or 8030 or Dynaudio bm6A mk2 for much more precision etc.

i've seen on the Genelec site(thanks to Subfunk)that you can determine the right kind of monitor by taking room size into account,plus listening distance.

i'm just really curious what exactly happens if you have one of these scenarios :

-too big monitors in a small room.
-too small monitors in a big room.

(both without subwoofer,since everyone advised me NOT to use those,especially in a small room)



thanks!