The calculation is simple: Total stored size divided by total number of purchased licenses.
Total stored size is how much storage is consumed on Spanning side. This is your data after compression and de-duplication.
1 TB = 1024 GB
A customer is currently storing 10TB of combined data in Spanning for their domain.
Total number of purchased licenses is 200.
10 TB * 1024 = 10,240 GB.
10,240 GB / 200 licenses = 51.2 GB / license.
Note: At this time due to how Team Drives and Shared Drive data is provided to Spanning, it is not possible to isolate from Spanning's side which user or shared drive may be individually contributing to a large data set. Furthermore as Spanning retains all versions of all historical data, we will not report the same sizes you may see in Google's UI which reflects only the current data a user holds. Additional information on how Spanning retains data is covered in this article: Why does Spanning’s data storage amount vary from what’s shown in your Google Workspace storage?