I provided a command to see do you have pieces older than 7 days.
If you just want to see how much it takes in total, you need to use an du -s --si /mnt/storj/storagenode/storage/trash command instead, where /mnt/storj/storagenode is a path to your data location.
The information on the dashboard is taken from the databases. So if your databases are ok (you may check that: https://support.storj.io/hc/en-us/articles/360029309111-How-to-fix-a-database-disk-image-is-malformed), then you probably have issues with filewalkers or the used-space-filewalker is disabled (it’s enabled by default). If you have errors related to any of filewalkers (search for walk|retain|trash and error|failed|ERROR), then I would suggest to enable a used-space-filewalker on startup and disable a lazy one:
Do not forget to save the config and restart the node.