A hair's breadth, or the width of human hair, is used as an informal unit of a very short length. It connotes "a very small margin" or the narrowest degree in many contexts.
This measurement is not precise because human hair varies in diameter, ranging anywhere from 17 μm to 181 μm [millionths of a metre] One nominal value often chosen is 75 μm, but this – like other measures based upon such highly variable natural objects, including the barleycorn – is subject to a fair degree of imprecision.
Such measures can be found in many cultures. The English "hair's breadth" has a direct analogue in the formal Burmese system of Long Measure. A "tshan khyee", the smallest unit in the system, is literally a "hair's breadth". 10 "tshan khyee" form a "hnan" (a Sesamum seed), 60 (6 hnan) form a mooyau (a species of grain), and 240 (4 mooyau) form an "atheet" (literally, a "finger's breadth").
Some formal definitions even existed in English. In several systems of English Long Measure, a "hair's breadth" has a formal definition. Samuel Maunder's Treasury of Knowledge and Library of Reference, published in 1855, states that a "hair's breadth" is one 48th of an inch (and thus one 16th of a barleycorn). John Lindley's An introduction to botany, published in 1839, and William Withering' An Arrangement of British Plants, published in 1818, states that a "hair's breadth" is one 12th of a line, which is one 144th of an inch or ~176 μm (a line itself being one 12th of an inch).
Other body part measurements
Winning a competition, such as a horse race, "by a whisker" (a short beard hair) is a narrower margin of victory than winning "by a nose." An even narrower anatomically-based margin might be described in the idiom "by the skin of my teeth," which is typically applied to a narrow escape from impending disaster. This is roughly analogous to the phrase "as small as the hairs on a gnat's bollock." German speakers similarly use “Muggeseggele,” literally “housefly’s scrotum,” as a small unit of measurement.
- List of humorous units of measurement
- List of unusual units of measurement
- Indefinite and fictitious numbers
- ^ "Hair's breadth (hare's breath)". Grammarist. 10 February 2011. Retrieved January 27, 2015.
- ^ Hairs breadth. Oxford English Dictionary. Archived from the original on February 3, 2015. Retrieved January 28, 2015.
- ^ "Hairs breadth". Macmillan English Dictionary. Retrieved January 27, 2015.
- ^ "Hairs breadth". Cambridge Dictionary. Retrieved January 27, 2015.
- ^ a b c Smith 2002, p. 253.
- ^ a b Crook & Osmaston 1994, p. 133.
- ^ a b Johnson 1842, pp. 1257.
- ^ Ley, Brian (1999). Elert, Glenn (ed.). "Diameter of a human hair". The Physics Factbook. Retrieved 2018-12-08.
- ^ Boaz, Tilloch & Taylor 1823, p. 267.
- ^ Latter 1991, pp. 167.
- ^ Carey 1814, p. 209.
- ^ Maunder 1855, p. 12.
- ^ Lindley 1839, p. 474.
- ^ Withering 1818, p. 69.
- ^ "Win by a nose". The American Heritage® Idioms Dictionary. Houghton Mifflin Company/Dictionary.com. 2002. Retrieved January 27, 2015.
- ^ "By a nose". Free Dictionary. Retrieved December 30, 2016.
- ^ "The meaning and origin of the expression: By the skin of your teeth". The phrase finder. Retrieved January 28, 2015.
- ^ Sellner, Jan (9 March 2009). "Schönstes schwäbisches Wort: Großer Vorsprung für Schwabens kleinste Einheit". Stuttgarter Nachrichten (in German). Archived from the original on 27 September 2013. Retrieved 13 August 2013.
- Boaz, James; Tilloch, Alexander, Editor; Taylor, Richard, Editor (1823-03-21). "On a fixed Unit of Measure". Philosophical Magazine. Vol. 61. London: Richard Taylor. p. 267.
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