SharePoint - Various way to get the size at the site collection and its various level

We have many times the requirement to get the size at various level in SharePoint – Hope the below information will help you !!

SharePoint Designer –

Specific feature of it – the ability to view the storage used for an entire site collection!

If you open up SharePoint Designer to the root site of your site collection, in the main window, once the site is opened under Site Information, that it will conveniently display the Total Storage Used of your entire site collection!

StorMan.aspx –

SharePoint 2010
Go to Site Actions -> Site Settings -> Site Collection Administration -> Storage Metrics, this will give you details on the usage – such as what sites, lists, libraries, and items are taking up the most space, however, it will not give you a total like our trusty SharePoint Swiss Army Knife – SharePoint Designer does, but, it will allow you to drill down into the usage.

PowerShell
$site = Get-SPSite http://my.sitecollection.com
$site.Usage;
$site.Dispose();

$site = Get-SPSite http://my.sitecollection.com
$site.Usage.Storage;
$site.Dispose();

Web Analytics
Go to Site Actions -> Site Settings -> Site Actions -> Site Collection Web Analytics reports

Once there, in the main screen, you can view a summary of the Total Storage Used under Inventory

And if you click on Storage Usage under Inventory within the quick launch navigation on the left, you can then view reports on storage utilization for your site collection, with a graph of the values so you can easily visualize the trend in storage usage.

You can also run reports for any date range since Web Analytics have been enabled, as well as run workflows against this data for alerting and reporting.