Hard to answer without specifying a particular option since each option has a different SPAN margin. The basic margin parameters used for ZB options are: range $3,750 and vol scan 0.025. You can get a pretty good estimate of the margin if you can value the option at the 16 scenarios used by SPAN defined by those parameters.
You can also download a huge text file from the CME showing margin details for every option. While the file's intended for machine reading, it's possible to manually read the file with some effort.
