Here is a PowerShell function helpful in populating statistics of sub-folder sizes.

1. Create a PS1 file named Get-FolderSize.ps1 with the following contents:

Function Get-FolderSize

{

 BEGIN{$fso = New-Object -comobject Scripting.FileSystemObject}

 PROCESS
    {

    $path = $input.fullname

    $folder = $fso.GetFolder($path)

    $size = $folder.size

    [PSCustomObject]@{‘Name’ = $path;’Size’ = ($size / 1gb) }

    } 
}

2. Launch Powershell and import the new PS1 file we create using CMDLET

Import-Module Get-FolderSize.ps1

3. Traverse into the parent folder you wish to query using the CD command.

4. Execute CMDLET

Get-ChildItem -Directory -EA 0 | Get-FolderSize | sort size -Descending

You can now manually consolidate output into an Excel spreadsheet and even calculate totals/average.