[Jwarder]

I don't think the issue is with the number, but rather the context. What should the end user think when finder reports that there is 60TB of data on a 2TB drive? People with above average file system knowledge can generate an explanation for it, but what good does that number do?

When programming a feature like this it can be hard to spot the problem. The calculations for the backup's size can be 100% right, but still not appropriate to show.