How much space is my google account ACTUALLY taking up?

I use Gmail and Google Drive for work (at a public school in the US). When I enter Drive and open settings, my storage reports this:

This looks to be about right to me, as I have several large audio/video files that take up a significant amount of space.

But when I look at the little readout at the bottom my of Gmail inbox, it shows this:

I can't imagine how I would ever take up 22,000 GB of space! So, what's going on here?