Actually, jcoolkatzerg, that's not correct.

FAT-formatted disks are set up so that a file must take up at least one disk allocation unit. Depending on the size of the unit, this could mean that a one-byte file takes up 4KB on disk. Files also cannot share allocation units. So if you have a bunch of one-byte files on a disk with 4KB units, they'll each take up 4KB. This could mean that 100 bytes' worth of data takes up 400KB on disk.

"Size on disk" is the total size of all the allocation units used by the data for which you're getting the properties.

And yes, there's a way around it: Format your disk with a smaller allocation unit size. However, the smaller the allocation unit, the more each file will take up, so the longer it'll take to read/write the disk.