Scanning electron microscope image of a human hair

A hair's breadth, or the width of human hair, is used as an informal unit of a very short length.[1] It connotes "a very small margin" or the narrowest degree in many contexts.[2][3][4][5][6][7]

## Definitions

This measurement is not precise because human hair varies in diameter, ranging anywhere from 17 μm to 181 μm.[8] One nominal value often chosen is 75 μm,[5] but this – like other measures based upon such highly variable natural objects, including the barleycorn[9] – is subject to a fair degree of imprecision.[5][7]

Such measures can be found in many cultures. The English "hair's breadth"[6] 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").[10][11]

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).[12] 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 (a line itself being one 12th of an inch).[13][14]

## 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."[15][16] 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 idiomatic phrase "as small as the hairs on a gnat's bollock."[17] German speakers similarly use “Muggeseggele,” literally “housefly’s scrotum,” as a small unit of measurement.[18]

## References

### Citations

1. ^ "Hair's breadth (hare's breath)". The Grammarist. Retrieved January 27, 2015.
2. ^ Hairs breadth. Oxford English Dictionary. Retrieved January 28, 2015.
3. ^ "Hairs breadth". Macmillan English Dictionary. Retrieved January 27, 2015.
4. ^ "Hairs breadth". Cambridge Dictionary. Retrieved January 27, 2015.
5. ^ a b c Smith 2002, p. 253.
6. ^ a b Crook & Osmaston 1994, p. 133.
7. ^ a b Johnson 1842, pp. 1257.
8. ^ Ley, Brian (1999). Elert, Glenn (ed.). "Diameter of a human hair". The Physics Factbook. Retrieved 2018-12-08.
9. ^ Boaz, Tilloch & Taylor 1823, p. 267.
10. ^ Latter 1991, pp. 167.
11. ^ Carey 1814, p. 209.
12. ^ Maunder 1855, p. 12.
13. ^ Lindley 1839, p. 474.
14. ^ Withering 1818, p. 69.
15. ^ "Win by a nose". The American Heritage® Idioms Dictionary. Houghton Mifflin Company/Dictionary.com. 2002. Retrieved January 27, 2015.
16. ^ "By a nose". Free Dictionary. Retrieved December 30, 2016.
17. ^ "The meaning and origin of the expression: By the skin of your teeth". The phrase finder. Retrieved January 28, 2015.
18. ^ 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.