VM Guest HDD percentage

$report1 = Get-Datastore "yyyyyy" |Get-VM |

Select Name,

@{N="GuestUsageGB";E={[math]::Round(($_.Guest.Disks | %{$_.CapacityGB - $_.FreeSpaceGB} | Measure-Object -Sum | Select -ExpandProperty Sum),1)}},

@{N=“GuestCapacityGB";E={[math]::Round(($_.Guest.Disks | %{ $_.Capacity / 1GB} | Measure-Object -Sum | Select -ExpandProperty Sum),2)}},

@{N=“FreeSpaceGB";E={[math]::Round(($_.Guest.Disks | %{ $_.FreeSpace / 1GB} | Measure-Object -Sum | Select -ExpandProperty Sum),2)}},

@{N="GuestUsage(%)";E={[math]::Round(($_.Guest.Disks | %{ 100-(100*($_.FreeSpaceGB / $_.CapacityGB))} | Measure-Object -Average | Select -ExpandProperty Average),2)}},

@{N='SnapshotSizeGB';E={[math]::Round((Get-Snapshot -VM $_ | Measure-Object -Property SizeGB -sum).Sum,2)}}

$sum = $report1 | Measure-Object -sum "GuestUsageGB","GuestCapacityGB",“FreeSpaceGB"

$row = "" | Select "GuestUsageGB","GuestCapacityGB",“FreeSpaceGB"

$row."GuestUsageGB" = 'Total'

$row."GuestUsageGB" = $sum | where{$_.Property -eq "GuestUsageGB"} | select -ExpandProperty Sum

$row."GuestCapacityGB" = $sum | where{$_.Property -eq "GuestCapacityGB"} | select -ExpandProperty Sum

$row."FreeSpaceGB" = $sum | where{$_.Property -eq "FreeSpaceGB"} | select -ExpandProperty Sum

$report1 += $row

$report1 | export-csv VMHDD_REPORT_$datefile.csv -NoTypeInformation

I am using the above script to get Guest HDD usage but having issue at (Guestusage %) percentage, its not providing the correct values.