Hi Anh,
If you talk to Support, please follow back here with the resolution for the thread. In the meantime, I'd expect a SUM of the value called [Seat Count] to give you that number. From help:
Seat Count: The number of seats (inventory) for a product. Only price layers in the Ticket Price price category are counted for this field. If multiple Ticket Price price layers exist for a performance, the Ticket Price price layer with the min start date and min price layer type rank is counted. If you break out counts by price layer, layers in all other categories will have a count of 0.
One caveat to that is this setting: Include Blacked Out Seats. When set to No (the default) seats that are held with a blackout hold code are not included in Tessitura Analytics. Setting this entry to Yes will include seats held with blackout hold codes in unsold seat counts and capacity calculations. If you include them, you can filter them out with a Hold Code filter on the widget or dashboard that is set to exclude the kill holds.
I would avoid using Ticket Count as a method of counting the sold segmentation of your seat capacity, as a single seat could be sold multiple times (benevolent returns), and a ticket could be unseated and still count toward an overall sold ticket count.
A similar issue can occur with distinct counts of Perf Seat Key, Seat Key, and Seat ID as tickets without seats will still have a placeholder value (e.g. -999999) that will contribute to the overall total unique count of values.
Best,Chris