Get File Size

I want Opus to get file sizes every time the display in a lister changes (auto).
File sizes, not folder sizes. Then I can use the get sizes button on selected folders.
How come it can auto get folder sizes but not file sizes?

File sizes are always shown. I'm not quite sure what you're asking.

That explains why 'files' don't appear in the options.
I assumed the files sizes were showing up because I had the always calculate sizes enabled, sorry.