Inch
A unit of length in Imperial and US customary systems.
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The inch (abbreviated as in or ″) measures length in both the British Imperial and United States customary systems. It equals 1/36 of a yard or 1/12 of a foot. Its name comes from the Roman uncia (“twelfth”), and the word is often used to translate similar units in other systems, typically linked to the width of a human thumb. Over time, the inch’s exact length has shifted, but since the international yard was adopted in the mid-20th century, it has been defined as exactly 25.4 mm, based on the metric system.
Name
The English word "inch" was borrowed early from the Latin uncia, meaning one-twelfth, a Roman inch, or an ounce. The vowel shift from Latin u to Old English y (which became modern English i) is known as umlaut, while the consonant change from Latin c to English ch is palatalisation, both features of Old English phonology. "Inch" is cognate with "ounce," whose separate pronunciation and spelling reflect a later reborrowing in Middle English from Anglo-Norman. In many European languages, the word for "inch" is the same as or derived from the word for "thumb," as a man's thumb is about an inch wide, and this was sometimes used to define the inch. Examples include Swedish tum (inch) and tumme (thumb), Danish tomme (inch) and tommel (thumb), Dutch duim (inch and thumb), and Czech palec (inch and thumb).
History
The earliest known reference to the inch in England is from the Laws of Æthelberht, dating to the early 7th century, surviving in a single manuscript from 1120. It set fines for wounds of various depths: one inch, one shilling; two inches, two shillings. An Anglo-Saxon unit was the barleycorn, and after 1066, one inch equaled three barleycorns, a legal definition for centuries.
A 1324 statute of Edward II defined the inch as "three grains of barley, dry and round, placed end to end, lengthwise." Similar definitions appear in Welsh medieval law tracts from the Laws of Hywel Dda. King David I of Scotland, around 1150, defined the Scottish inch as the width of an average man's thumb at the base of the nail, requiring an average of small, medium, and large men. In 1814, mathematics teacher Charles Butler recorded the old legal definition as three grains of sound ripe barley from the middle of the ear, well dried, laid end to end, placing the barleycorn as the base unit of English Long Measure.
Lore & Background
The English word 'inch' (Old English: ynce) was an early borrowing from Latin uncia ('one-twelfth; Roman inch; Roman ounce'). The vowel change from Latin /u/ to Old English /y/ (which became Modern English /ɪ/) is known as umlaut, and the consonant change from Latin /k/ to English /tʃ/ is palatalisation. 'Inch' is cognate with 'ounce', whose separate pronunciation and spelling reflect its reborrowing in Middle English from Anglo-Norman unce and ounce. In many other European languages, the word for 'inch' is the same as or derived from the word for 'thumb', as a man's thumb is about an inch wide.
Paragraph LXVII sets out the fine for wounds of various depths: one inch, one shilling; two inches, two shillings, etc. An Anglo-Saxon unit of length was the barleycorn. Similar definitions are recorded in both English and Welsh medieval law tracts.
Reader's Guide
The inch remains a commonly used customary unit of length in the United States, Canada, and the United Kingdom. For the United Kingdom, guidance on public sector use states that, since 1 October 1995, without time limit, the inch (along with the foot) is to be used as a primary unit for road signs and related measurements of distance. Inches are used for display screens (e.g. televisions and computer monitors) worldwide, and are the official Japanese standard for electronic parts, especially display screens. They are also commonly used to specify the diameter of vehicle wheel rims and the corresponding inner diameter of tyres.
The international standard symbol for inch is 'in', but traditionally the inch is denoted by a double prime, often approximated by a double quote symbol. Subdivisions of an inch are typically written using dyadic fractions with odd number numerators. The inch's definition has evolved from barleycorns and thumb widths to an exact metric equivalent of 25.4 mm, adopted during the 1950s and 1960s with the international yard.
Frequently Asked Questions
Who is Inch?
Inch is a unit of length that serves as a foundational member of both the British Imperial and United States customary measurement systems. It occupies the position of one-twelfth of a foot or one-thirty-sixth of a yard, making it a key building block in those frameworks.
What is Inch known for?
Inch functions as a practical subdivision for measuring shorter distances, sitting between the foot and the yard in Imperial and US customary use. Its symbol appears as either the abbreviation "in" or the double-prime mark (″), and it remains the standard reference for many everyday measurements in the United States.
Where does Inch come from?
The name traces back to the Latin word "uncia," meaning "twelfth," reflecting its original role as one-twelfth of a foot. The earliest English reference to the unit appears in the Laws of Æthelberht from the early 7th century, and folk etymology often links the concept to the width of a human thumb.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Inch (CC BY-SA 4.0).
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