Database snapshot files are sparse files that show an allocated size the same size as the database file that are a snapshot of, but typically use much less space on disk.

If you open Windows Explorer, right click on the snapshot file, and click properties, you will see numbers for "Size", and "Size on Disk".

The "Size on Disk" is the amount of space that it is actually using, while the "Size" is the size it will grow to if necessary.

The size of the database backup file is related to the amount of data in the database, not the size of the database files.