Counting the licensing usages and checking out the license details in Office 365 using PowerShell is a lot easier than going through the admin console.
First, install the module if you haven’t done, and connect to Azure AD with your Office 365 subscription.
Install-Module msonline Connect-MsolServie
To list of the licensing plans available in my tenant:
Get-MsolAccountsku
To view a full list of licensed accounts:
Get-MsolUser | Where {$_.IsLicensed}
How many of my users are licensed in Premium?
Get-MsolUser | Where {($_.Licenses).AccountSkuID -eq $accountskuid}
Where $accountskuid can be found in the cmdlet Get-MsolAccountsku described above.
Need to export the result in CSV for reporting purpose?
Get-MsolUser | Where {($_.Licenses).AccountSkuID -eq $accountskuid} | Export-CSV "path\csvname"