On a typical housecat, how long are its whiskers compared to its body length?

Answer 1

i'd say about twice the width of the cats face.

whiskers are actually used to tell the distance of an opening that cat might try to go through. they tell him if he can fit or not. (they do other things too, but this seems to relate most to what you're asking.)

Answer 2

Cats' whiskers are independent of length of the body. However, they are approximately as long as the width of the body. That is, they extended out on both sides for a total width of the body.

Cats use them to maneuver and figure out if they can walk through a space (i.e., if they can't fit their whiskers through, they won't try to fit their body's through).