According to my "units" program, a "biblicalcubit" is 21.8 inches, and a "hebrewcubit" is 17.58 inches. That's a great deal of variance.
$ grep -i cubit /usr/share/units.dat pied frenchfoot # Half of the hashimicubit, irishcubit 18 irishinch romancubit 18 romaninch # units. egyptianroyalcubit 20.63 in # plus or minus .2 in egyptianpalm 1|7 egyptianroyalcubit egyptianshortcubit 6 egyptianpalm remendigit 1|40 doubleremen # side length of 1 royal egyptian cubit. # the royal cubit. greekfeet greekfoot # Egyptian Royal cubit in [11]. It is greekcubit 1.5 greekfoot # said to be 3|5 of a 20.75 in cubit. homericcubit 20 greekfingers # Elbow to end of knuckles. shortgreekcubit 18 greekfingers # Elbow to start of fingers. olympiccubit 25 remendigit # These olympic measures were not as olympicfoot 2|3 olympiccubit # common as the other greek measures. # "Northern" cubit and foot. This was used by the pre-Aryan civilization in northerncubit 26.6 in # plus/minus .2 in northernfoot 1|2 northerncubit sumeriancubit 495 mm kus sumeriancubit sumerianfoot 2|3 sumeriancubit assyriancubit 21.6 in assyrianfoot 1|2 assyriancubit persianroyalcubit 7 assyrianpalm hashimicubit 25.56 in # Standard of linear measure used blackcubit 21.28 in arabicfeet 1|2 blackcubit arabicmile 4000 blackcubit biblicalcubit 21.8 in hebrewcubit 17.58 in
That didn't really format well, but it is interesting nonethelss.
OK, so which is it?