The biggest factor is in fact that the drive manufacturers quote in billion bytes (ie, 1,000,000,000 bytes per GB) and emplode counts in computer-GB (ie 2^30).

36 disk-drive manufacturer GB = 33.5 emplode GB

ISTR that's the GB we use in the calculation anyway. Would exactly explain your situation. The formatting overhead of ext2 is pretty small (especially if you do as we do and use "-i131072 -m0 -s1" flags to mke2fs which puts less inodes and superblocks on the disk)

Hugo