The following PowerCLI code will give you the provisioned space in GB for each datastore:
Get-Datastore |Select-Object-Property Name, CapacityGB,FreeSpaceGB, @{ Name ="ProvisionedSpaceGB" Expression = {($_.ExtensionData.Summary.Capacity -$_.Extensiondata.Summary.FreeSpace +$_.ExtensionData.Summary.Uncommitted)/1GB} }