A finger (sometimes fingerbreadth or finger's breadth) is any of several units of measurement that are approximately the width of an adult human finger. [Exactly which part of the finger should be used is not defined; the width at the base of fingernail (#6 in the sketch) is typically less than that at the knuckle (#5).]
The digit, also known as digitus or digitus transversus (Latin), dactyl (Greek) or dactylus, or finger's breadth of an inch or of a foot.[1] [2] (about 2 cm)
In medicine and related disciplines (anatomy, radiology, etc.) the fingerbreadth (literally the width of a finger) is an informal but widely used unit of measure.[3] [4]
In the measurement of distilled spirits, a finger of whiskey refers to the amount of whiskey that would fill a glass to the level of one finger wrapped around the glass at the bottom.[5] [6] [7]
Another definition (from Noah Webster): "nearly an inch."[8] [9]
Finger is also the name of a longer unit of length, used historically in cloth measurement, to mean one eighth of a yard or 4 inches.[10] (114.3 mm) Again, which finger and whose finger, is not defined.
These units have no legal status but remain in use for 'rough and ready' comparisons.
. Ronald Edward Zupko. Ronald Edward Zupko. A dictionary of weights and measures for the British Isles: the Middle Ages to the twentieth century. 1985 . American Philosophical Society . 978-0-87169-168-2. 109–10.
. Bret Harte. Bret Harte. McClure's magazine. https://books.google.com/books?id=ZmlXbZ0w2wYC&pg=RA1-PA230 . 1899 . S.S. McClure Co. . 230 . A Jack and Jill of the Sierras.
. Noah Webster. Noah Webster. Webster's collegiate dictionary. 14 January 2012. 1896. G. & C. Merriam. 332.