The unit described on this page was in use prior to modern methods of precision measurement. It was based on a standard which is no longer available, and which is not capable of being calibrated against modern measurement units. Therefore, the equivalence to modern SI units or to current United States customary units can only be considered approximate.
Ancient Hebrew units of length or distance are mentioned in the Bible, but their values in terms of modern units are open to some speculation. The only way of determining the length of any Ancient Hebrew unit would be to measure something in modern terms whose length was given by the Hebrews in their units. Unlike the Attic Greek and Ancient Roman units, there are not good examples of such measurable objects, so much of the information we have is based on guesswork.
The range of values of the length of the tefach given in various sources gives the minimum as 8 cm = 3.15 in. = 0.26 ft and the maximum as 10.67 cm = 4.2 in. = 0.35 ft .