How do you calculate social share counts?

All the share counts come via the network's API.

How the numbers are calculated varies depending on the network; for example, Google+ combine essentially any social action taken on the shared link.

Since this data is only available at the URL level, all social shares at the 'Domain Level' are simply the share counts for the homepage URL.

Here is how each is one is worked out:

Domain Level Data

Homepage Google Plus Ones - The number of times the homepage URL has been had the +1 button clicked, plus the number of times the URL has been shared/reshared on Google+, plus any +1 of those shares or comments.
Homepage LinkedIn Shares - The number of times the homepage URL has been included in a LinkedIn share.
Homepage Pinterest Pins - The number of times an image on the homepage URL has been pinned or repinned.
Homepage Total Shares- The total number of shares of the homepage URL, as above (however, this is also based on which social networks you choose to select in the settings).

URL Level Data

URL Google Plus Ones - The number of times the URL has been had the +1 button clicked, plus the number of times the URL has been shared/reshared on Google+, plus any +1 of those shares or comments.
URL LinkedIn Shares - The number of times the URL has been included in a LinkedIn share.
URL Pinterest Pins - The number of times an image on the URL has been pinned or repinned.
URL Total Shares - The total number of shares of the URL, as above (however, this is also based on which social networks you choose to select in the settings).