Get GUID Sharepoint

Open “SharePoint 2010 Management Shell”  (PowerShell for SharePoint)
Enter:
$site = Get-SPSite  http://yourserver/sites/yoursitename
$web = $site.AllWebs[“yoursubsitename”]     or  $site.RootWeb   for the root site
$web.ID
Guid
—-
f70832a4-5d0d-4265-a344-ea10a0007160