How do you see file size in GB?

go to folder where files exits

$cd /tmp/backup_folder

$ du -ahl
17G ./fullback.cpio
.

ex:
suresh:tmp/willardbackup$ du -ahl
4.1G ./fullback01
2.1G ./fullback03
15G ./fullback.cpio
4.1G ./fullback02
4.1G ./fullback00
4.0K ./fullback.md5
29G