The barleycorn has been the basis of units of length and mass in a number of systems of units.
In England and Scotland, at least as early as the 12ᵗʰ century an inch was thought of as 3 barleycorns laid end to end. A document of 1474 states: “Also hitt was ordeyned at the same tyme that iij barley-Cornes take out of the middes of the Ere makith a Inche; and xij Inches makith a foote, and iij fote makith a yarde.”¹ Occasionally “barleycorn” was used to mean one-third of an inch. It is still true that 36 barleycorns laid end to end closely approximate a foot, but legally the inch was always derived by subdividing such prototypes as the “king's iron yard.”
Ibn Khurrâdadhbih, writing in the 9ᵗʰ century, reported that the smallest unit of length in Islamic measure, the aasbaa, literally “finger,” was the width of 6 barleycorns laid side by side.
The grain, ¹/₅₇₆₀th of the troy pound and the apothecaries' pound, and ¹/₇₀₀₀th of the pound avoirdupois, is traditionally the weight of a barleycorn. Before the development of the modern strains of wheat and barley, the ratios 3 barley corns = 4 grains of wheat, 4 grains of wheat = 1 carob seed (siliqua) were used in many systems of weight. For example, as the se, the barleycorn was a standard of mass in ancient Sumeria.
1. Mary Dormer Harris, transcriber and editor.
The Coventry Leet Book: or Mayor's Register. Part 1.
Early English Text Society series 134.
London: Kegan Paul, Trench, Trübner & Co., 1907.
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Last revised: 8 March 2008.