Go to [System Information] section and look for "Local disk space" in [Sytem Information] tab. In my case it reports 12.50 GB used, 94.40 GB total. See the image in attachment.
When I check the disk usage in Terminal I get other values. The difference is notable: Size 95G, Used 7.8G. See the other image in attachment. There are 4.7 GB which Webmin shows as being used. This value is wrong and it could be a bug.
I did a refresh but nothing changes.