Ancient units of measure were done differently according to where one resided. A good example would be Greece and Rome which both utilized the Hellenic system of measurement. To further complicate things, this Hellenic system was actually based upon an ancient Egyptian and Mesopotamian system of measurement.
Here are a few examples of ancient measurements:
28th part of a cubit. Width of a finger. Approx.
To steal (slang). Rhyming slang for "pinch."
10 lines. 1000 thou. or mils. Width of man's thumb, length of 3 barley corns (Anglo-Saxon).
3 inches. Width of man's palm.
4 inches. Width of man's hand; used for height of horse at its withers (shoulders). Formerly, approx. 5 inches.
6 inches. 6½ inches until 12th Century.
9 inches. Width of man's spread fingers.
9.8 inches (approx). Anglo-Saxon.
As you can clearly see, it would be dependent upon what one was measuring and where one resided. There are more examples like above  below.