unfortunately, AIX doesn't offer the '-h' flag for the df command.
if you want the output more readable in terms of megabytes or gigabytes (and if you're using a recent version of AIX... i think 5.2 or later)... try the 'df -m' or 'df -g' commands. '-m' will list the output in megabytes and '-g' will list in gigabytes. unfortnutely, i don't think there's a way to combine it like how '-h' would.