Get-MailboxDatabase cmdlet comes in handy to check all mailbox database size quickly. Help for this cmdlet is available here: http://technet.microsoft.com/en-us/library/bb124924.aspx
Here is the command and run it in Exchange Management Shell.
Get-MailboxDatabase -Status | select ServerName,Name,DatabaseSize
I am trying to write a script to gather database size every week and save it in one CSV file. I would like to see how my database are growing; take actions accordingly. Let me know if anyone interested in my script.