Checking the size of the mailbox database is not easy in Exchange 2007. This is because of the fact that Get-MailboxDatabase doesn’t have the a databasesize attribute when used with the –Status switch.
Fortunately, things have changed in Get-MailboxDatabase command in Exchange 2010. In order to find the size of mailbox databases, run the following command
Get-MailboxDatabase –Status | fl name, databasesize
Good that the command has been improved in 2010 to give the functionality out of the box!