man df
-B, --block-size=SIZE
use SIZE-byte blocks
-h, --human-readable
print sizes in human readable format (e.g., 1K 234M 2G)
-H, --si
likewise, but use powers of 1000 not 1024
SIZE may be (or may be an integer optionally followed by) one of following: kB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on
for G, T, P, E, Z, Y.