This Exchange Shell cmdlet will produce a report of all Public Folders in the organization with the full size.
Get-PublicFolderStatistics -resultsize unlimited | ft Name,DatabaseName,TotalAssociatedItemSize > c:\report.txt
The last part (> c:\report.ext )will Export the file to a Text file which can be exported to Excel, alternatively you can remove that part If you don’t want to export the output to a Text file.