And off my Mandrake 8.1 :

[pete@rotor pete]$ df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/hda1               248964    119884    129080  49% /
/dev/hda8               240928     34780    206148  15% /boot
none                    192212         0    192212   0% /dev/shm
/dev/hda12             6152668   2826800   3325868  46% /home
/dev/hda11             3622508     98152   3524356   3% /opt
/dev/hda6              4176736   2013256   2163480  49% /usr
/dev/hda7               329284    130696    198588  40% /var
/dev/hda9              2273088     32840   2240248   2% /var/ftp
/dev/hda10             2104408     42516   2061892   3% /var/www
[pete@rotor pete]$ df -b
df: invalid option -- b
Try `df --help' for more information.
[pete@rotor pete]$ df -B
df: invalid option -- B
Try `df --help' for more information.
[pete@rotor pete]$ df -B MB
df: invalid option -- B
Try `df --help' for more information.
[pete@rotor pete]$