How to tell how much RAM is being used?

[DannyITR]

Hello,

I'm going to be building a new I7-920 system and cannot decide if I need 6 gigs or 12 gigs of RAM. Is there any way to tell how much RAM my current 4gb system uses? I use photoshop, outlook, firefox etc at the same time and then play the occasional MW2 or FSX game.

 

[roonj]

taskmanager, performance, any free ram?, this is by no means accurate but!