Retrieve disk space used by files and subfolders of a given folder (in GB).

Get-FolderUsage

function Get-FolderUsage([String]$Folder) {
    [PSCustomObject]@{
        FullName=Join-Path -Path $Folder -ChildPath '*';
        SizeGb=[int]((Get-ChildItem -File $Folder | Measure-Object -Property Length -Sum).Sum / 1GB)
    } | Write-Output

    Get-ChildItem -Directory -Path $Folder |
        ForEach-Object {
            [PSCustomObject]@{
                FullName=$_.FullName;
                SizeGb=[int]((Get-ChildItem $_.FullName -Recurse | Measure-Object -Property Length -Sum).Sum / 1GB)
            } | Write-Output
        }
}

Set-Alias gfu -Value Get-FolderUsage