Here’s a script to grab the instance count for your app service plans:

  
$rg = read-host "Whats the rg?: "
  
write-host "getting plans for rg $rg"

try
  
{
      
$plans = Get-AzureRmAppServicePlan -ResourceGroupName $rg
  
}
  
catch
  
{
      
write-host "Unable to get plans! exiting"
  
}

$array = @()
  
foreach ($plan in $plans)
  
{
      
write-host "Getting app service plan $($plan.ServerFarmWithRichSkuName)"
      
$id = Get-AzureRmAppServicePlan -ResourceGroupName $rg -Name $plan.ServerFarmWithRichSkuName
      
$res = Get-AzureRmResource -ResourceId $id.Id

write-host "adding details to obj for output"
      
$obj = New-Object System.Object
      
$obj | add-member -MemberType NoteProperty -Name "name" -Value $plan.ServerFarmWithRichSkuName
      
$obj | add-member -MemberType NoteProperty -Name "instances" -Value $res.sku.capacity
      
$array += $obj
  
}
  
$array | ft