Get exchange database size

Get-MailboxDatabase -Status | select Name,DatabaseSize,AvailableNewMailboxSpace
 
Name                        DatabaseSize                    AvailableNewMailboxSpace
----                        ------------                    ------------------------
DB01                        23.25 GB (24,964,497,408 bytes) 123 MB (128,942,080 bytes)
DB02                        25.88 GB (27,783,069,696 bytes) 184 MB (192,970,752 bytes)
DB03                        3 GB (3,221,225,472 bytes)      58.03 MB (60,850,176 bytes)
DB04                        2.625 GB (2,818,572,288 bytes)  36.63 MB (38,404,096 bytes)
Mailbox Database 1833569659 768 MB (805,306,368 bytes)      179.8 MB (188,579,840 bytes)