Question / Problem
Why does TreeSize Free show different size values than Windows Explorer?
Answer / Solution
These differences can occur because the free version does not take all NTFS-specific features into account.
TreeSize Free recognizes compressed and sparse files. The new compression methods LZX and XPress, introduced with Windows 10, are supported with TreeSize Free v4.1 and above.
Features like Alternate Data Streams (ADS), Deduplication (Windows Server 2012 and above) or recognition of hardlinks are not evaluated in TreeSize Free.
The personal and professional edition come with an option to explicitly analyze these extended NTFS features, which may make the results more accurate.