Math Question- HELP!

[GenuineRisk]

Hey, math men and women- I'm writing a script about spiders and the movies' attempts to make them scary (I work for a zoo, remember) and I need some math help- one of the points in the script is that even the largest spider is still pretty small in relation to a human. The largest spider, (the Goliath Spider, if anyone's interested) can grow to 12 inches across (yes, pretty big, and gross if you step on it, but still crushable). What I need to know is, what fraction of a person's size is that? Say a 5'8" person, to strike a happy medium. A thirtieth the size of a person? Does anyone know how to figure that out?

I'll find the weight if that's necessary.

Thanks in advance!