Usb drive/memory stick space always insufficient..

I am currently in the process of wiping my laptop and am using a 16gb memory stick.

I have been using it to transfer individual files, however, I have now collected all files I wish to keep, and attempting to store them on the memory stick in the process.
When trying to drag them onto the memory stick, however, there continuously seems to be at least 1gb or less of free space. This started at around 17gb, and through deleting additional files, I am now down to 14gb of files and I’m still being prompted with this error message…
Sometimes, through deletion, there also seems to be an increase in the amount of storage space needed.

The usb drive is currently empty.