Size occupied by documents in server.

It looks like the Admin console only shows the size of the most current documents (i.e. excludes all versions). If you are pulling KC size then that would include all versions.

I tend to run the disk_usage.csv log under /data-metrics to look at the size of my document partitions to get this value.

Reference:
docs.appian.com/.../Appian_Administration_Console.html
docs.appian.com/.../Logging.html

In admin tab, Document Reports (Excluding versions) showing 2TB, and all communities showing 10GB, and data metrics showing 1.15 TB. Don't understand which one is correct. As per our Appian memory size we purchased, am thinking data metrics showing satisfying figures compared to others.
Thanks for your thoughts.

That is strange. I definitely would have thought that data-metrics is the most accurate but to be honest I don't have much experience with Document Reports. Given it is supposed to exclude version, it makes no sense to me that it would be larger than 1.15 TB. I suggest opening a support case with Appian and seeing if an engineer can confirm (maybe there is an issue with that report?)