Site quota management is very important to control the
resources in site collections. We all know that site quota can applied at the
site collection level only in SharePoint Server 2007 but now the question: is
it possible to set a storage quota on individual sub-sites within a site
collection in SharePoint 2010?
The answer is: the same situation persists in
SharePoint 2010 also. Quota
templates are applied at the site collection level in SharePoint 2010 as well.
To know the
complete details then please refer this: http://technet.microsoft.com/en-us/library/cc263223.aspx
Still if you wants to know how we can calculate the subsite storage then please let me know, Thank you