vCenter Server | How to get percentage free space of a datastore?

$vcenter = read-host "Enter vCenter server FQDN "

Connect-VIServer $vcenter

echo "Welcome to Datastore free space calculator tool"

echo ""

echo " Press 1 to search details for single datastore"

echo " Press 2 to search details for all the datastores"

$data = Read-Host "Enter your choice"

If($data -eq 1 )

{

$a= Read-Host " Please enter the name of DS"

$DS= Get-Datastore

Get-Datastore | where{$_.Name -eq $a} | Select @{N="DataStoreName";E={$_.Name}},@{N="Percentage Free Space(%)";E={[math]::Round(($_.FreeSpaceGB)/($_.CapacityGB)*100,2)}} | Where {$_."Percentage(<20%)" -le 20}

}

elseif ($data -eq 2 )

 { 

Get-Datastore | Select @{N="DataStoreName";E={$_.Name}},@{N="Percentage Free Space(%)";E={[math]::Round(($_.FreeSpaceGB)/($_.CapacityGB)*100,2)}} | Where {$_."Percentage(<20%)" -le 20}

}