The Collaborative International Dictionary of English v.0.48:

Handbreadth \Hand"breadth`\ (-br[e^]dth`), n.
   A space equal to the breadth of the hand; a palm. --Ex.
   xxxvii. 12.

   Syn: handsbreadth.
        [1913 Webster]

WordNet (r) 3.0 (2006):

handbreadth
    n 1: any unit of length based on the breadth of the human hand
         [syn: handbreadth, handsbreadth]

Easton's 1897 Bible Dictionary:

Handbreadth
   a measure of four fingers, equal to about four inches (Ex.
   25:25; 37:12; Ps. 39:5, etc.).