The following PowerShell script is a simple translation of the c# code in the accepted answer of the question How to get size of Azure CloudBlobContainer. Hope this suit your needs.
Login-AzureRmAccount
$accountName = "<your storage account name>"
$keyValue = "<your storage account key>"
$containerName = "<your container name>"
$storageCred = New-Object Microsoft.WindowsAzure.Storage.Auth.StorageCredentials ($accountName, $keyValue)
$storageAccount = New-Object Microsoft.WindowsAzure.Storage.CloudStorageAccount ($storageCred, $true)
$container = $storageAccount.CreateCloudBlobClient().GetContainerReference($containerName)
$length = 0
$blobs = $container.ListBlobs($null, $true, [Microsoft.WindowsAzure.Storage.Blob.BlobListingDetails]::None, $null, $null)
$blobs | ForEach-Object {$length = $length + $_.Properties.Length}
$length
Note: the leading Login-AzureRmAccount
command will load the necessary .dll for you. If you do know the path of "Microsoft.WindowsAzure.Storage.dll", you can replace it by [Reflection.Assembly]::LoadFile("$StorageLibraryPath") | Out-Null
. The path is usually like this "C:\Program Files\Microsoft SDKs\Azure.NET SDK\v2.7\ToolsRef\Microsoft.WindowsAzure.Storage.dll"