Param($DriveLetter)
if ($PSBoundParameters.Count -ne 1) { exit }

$DriveLetter = $DriveLetter.Substring(0,1)
try {
  $used = (Get-PSDrive -Name $DriveLetter -ErrorAction Stop).Used
  $free = (Get-PSDrive -Name $DriveLetter -ErrorAction Stop).Free
  $total= $used + $free
  return ($free / $total * 100)
}
catch {
  exit
}