On my laptop (Windows 10), I’m running low on storage on my C: drive, so I tried deleting a few things. After checking the properties of some files, I found one user folder that was taking up over 10GB of space. However, when I opened the folder and looked at the files inside, they only added up to about 1.2GB. I did the same thing with %appdata% and it only came to 1.2GB as well. How can I find out where all the extra space is being used? (Video in comments showing the problem)
You didn’t check the local appdata or locallow folders. There’s more than one hidden folder in your user directory. Try using a tool like Wiztree to see exactly which folder is taking up space.
@EricJohnson3
Oh, I didn’t know about those folders. Thanks for the tip, I’ll check that out. 
I suggest using a tool like TreeSize (Find Space Hogs with TreeSize Free | JAM Software). They have a free version that will help you see where the storage is being used. Be careful with deleting things from your user profile randomly. You can post the results here if you want more advice. It’s likely that a rogue app or temp files are taking up space, like Adobe or Outlook spamming local app data.
@ErrorHunterEthan
I mean, 10GB for an entire user folder is pretty small. My roaming appdata folder alone is 43GB lol
Have you tried running disk cleanup and selecting ‘clean up system files’? Let it rescan, then check all the options except ones you don’t want to erase (like previous Windows installations if you think you might downgrade). Then hit OK.