USB stick

Hi, I a 1GB USB stick and I want to put a 700MB file but my mac tells me that there is only 100MB free space but there is nothing on the stick. I have used it on a PC several times, what is the problem how do I fix it?
Thanks

It is one irritating thing with the Mac. You need to empty Trash with the stick attached. Deleted files are hidden on the stick and takes up space until you empty Trash.

I tried that but nothing still only 100MB

You sure you emptied the trash with the flash drive attached to the computer??

Try reformatting it using disk utility (in Utilities)

Make sure you select Dos format (FAT 32) if you want to use it for both mac and PC