This is how:

Get-Mailbox -ResultSize
Unlimited |
Get-MailboxStatistics |
Select DisplayName,servername,database,StorageLimitStatus,
@{name=”TotalItemSize (MB)”;expression={[math]::Round((($_.TotalItemSize.Value.ToString()).Split(“(“)[1].Split(” “)[0].
Replace(“,”,””)/1MB),2)}},@{name=”TotalDeletedItemSize (MB)”;expression={[math]
::Round((($_.TotalDeletedItemSize.Value.ToString()).Split(“(“)[1].Split(” “)[0].
Replace(“,”,””)/1MB),2)}},ItemCount,DeletedItemCount
| Sort “TotalItemSize (MB)”
 -Descending | Export-CSV “C:dirAll Mailboxes_120814.csv” -NoTypeInformation
Love it!