If you are receiving the error message "Your changes could not be saved because this SharePoint Web site has exceeded the storage quota limit.",  you are able to check the current SharePoint size and total storage used, by performing the following:

1. Log into SharePoint Site Collection as the Administrator. This will be the admin@domain.com credentials.

2. Select the Site Actions drop down and choose Site Settings.

3. Under 'Site Collection Administration' select Usage Summary. This will show you the amount of storage currently being used as well as the full storage amount.

Please note: You must be signed in as the Administrator to access these settings. Full Rights users will not be able to access this data.