# Iterate through all site collections in a SharePoint web application and output to a CSV file:
#  - Site, Size(B), Size(MB), Size(GB), Content database

$webApp = 'http://webappurl'
$csvPath = 'e:\data.csv'

# Get all the sites in the web app
$sites = Get-SPWebApplication $webApp | Get-SPSite -Limit ALL

# Set the header for the file
$data = "Site, Size(B), Size(MB), Size(GB), Content Database"

# Loop through each site pulling the data needed appending to $data
Foreach($site in $sites){
	$mb = "{0:F2}" -f($site.Usage.Storage/1024/1024)
	$gb = "{0:F2}" -f($mb/1024)
	$data += "`n" + $site.url + ", " + $site.Usage.Storage + ", " + $mb + ", " + $gb + ", " + $site.ContentDatabase.Name
}

# Output the data to the file
$data | out-file $csvPath