Hair's breadth

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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]

A "hair's breadth" was, and still is, informally, a very small measurement.[5][6][7]


This measurement is not a precise one. Human hair varies in diameter, ranging anywhere from 30 μm to 100 μm. One nominal value often chosen is 75 μm,[5] but this – like other measures based upon such highly variant natural objects, including the barleycorn[8] – 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").[9][10]

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).[11] 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).[12][13]

Red cunt hair[edit]

A subset of "hairs breadth" is the red cunt hair or RCH,[A][B] red pussy hair, and red one[C] which is a bawdy figure of speech used to represent very small widths.[D][E][19][20] It is a slang, tongue-in-cheek term that purports to describe a unit of measure, but is actually a subjective notion, and can change depending on the situation and context. At its core, it is a very small measurement.[21][22][23][24] The phrase is based on the concept of a pubic hair being small in diameter, and can be used to describe a minor adjustment necessary, and is akin to terms such as 'a tad', 'a smidgen', etc. The phrase is generally used to objectify small clearances, dimensions, or distances.[F] In usage, the terms "hair", "cunt hair" and "red cunt hair" are related and each one is considered smaller and more precise than the preceding one ("hair" being largest and "red cunt hair" being smallest).[G]

According to Sterling Johnson (1995) in English as a Second F**king Language "the term originated with master carpenters in New England, and is now universally used."[20] Other sources claim it originated in the late 1950s, as military slang.[24][27]

Other body part measurements[edit]

Winning a competition, such as a horse race, "by a whisker" (that is 'by a hair length') is a narrower margin of victory than winning "by a nose."[28][29] 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."[30] German speakers likewise have a small measurement, i.e. the Muggeseggele.[31]

See also[edit]



  1. ^ "'Oh, just another RCH,' replies the perfectionist. 'What's an RCH?' I naively inquire. The crew replies in chorus, 'Red Cunt Hair.' I was learning a wealth of technical jargon."[14]
  2. ^ "... a mortar round came in and missed you by an R.C.H. [an R.C.H. being survivors' lingo for something very thin—a Red Cunt Hair] and that sucker missed you by one of those."[15]
  3. ^ " one [...] a very short distance. A euphemized abbreviation of Red Cunt Hair. Red pussy hair — a very short distance. Slightly less offensive than Red Cunt Hair."[16]
  4. ^ "RCH (noun) a tiny notional unit of measure (US) An abbreviation of Red Cunt Hair, perceived as a smaller unit even than a simple Cunt Hair"[17]
  5. ^ "Small measurements are frequently referred to as 'just a cunt hair,' or, if more accuracy is preferred, as a 'red cunt hair' (no other color is ever used)."[18]
  6. ^ "Red cunt hair. A very small distance (as in, 'That is one red cunt hair out of alignment.'"[25]
  7. ^ "Bump it a little west now, a hair more, a cunt hair now ... a red cunt hair ... good."[26]


  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. ^ Boaz, Tilloch & Taylor 1823, p. 267.
  9. ^ Latter 1991, pp. 167.
  10. ^ Carey 1814, p. 209.
  11. ^ Maunder 1855, p. 12.
  12. ^ Lindley 1839, p. 474.
  13. ^ Withering 1818, p. 69.
  14. ^ Spelvin 2008, p. 110.
  15. ^ Michaelis 1983, p. 23.
  16. ^ Partridge, Dalzell & Victor 2008, p. 535.
  17. ^ Partridge, Dalzell & Victor 2008, p. 1596.
  18. ^ Dorson 1986, p. 123.
  19. ^ Partridge, Dalzell & Victor 2008, p. 1601.
  20. ^ a b Johnson 1995, pp. 81-82.
  21. ^ Fleischhauer, Carl (1968). A Glossary of Army Slang. p. 14. 
  22. ^ Dickson, Paul (September 1, 2010). Slang: The Topical Dictionary of Americanisms. Bloomsbury. p. 362. ISBN 9780802718495. USA Bawdy unit of measurement ... Same as Frog hair 
  23. ^ Dickson 2011, p. 86.
  24. ^ a b Dalzell & Victor 2013, p. 1843.
  25. ^ Dickson 1994, p. 286.
  26. ^ Hales 2005, p. 45.
  27. ^ Morton 2003, p. 134.
  28. ^ "Win by a nose". The American Heritage® Idioms Dictionary. Houghton Mifflin Company/ 2002. Retrieved January 27, 2015. 
  29. ^ "By a nose". Free Dictionary. Retrieved December 30, 2016. 
  30. ^ "The meaning and origin of the expression: By the skin of your teeth". The phrase finder. Retrieved January 28, 2015. 
  31. ^ 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.