Inch
An inch is the name of a
unit of length in a number of different systems, including English units,
Imperial units, and United States customary units. Its size can vary from system to system. There are 36 inches in a yard and 12 inches in a
foot. A corresponding unit of
area is the square inch and a corresponding unit of volume is the cubic inch.
The inch is the virtually universal unit of measurement in the
United States, and the
United Kingdom and is the most common unit of measurement in
Canada. In the US and the UK,
personal heights are expressed in feet and inches by people of all ages.
Encyclopedia
An
inch is the name of a
unit of length in a number of different systems, including English units,
Imperial units, and United States customary units. Its size can vary from system to system. There are 36 inches in a yard and 12 inches in a
foot. A corresponding unit of
area is the square inch and a corresponding unit of volume is the cubic inch.
The inch is the virtually universal unit of measurement in the
United States, and the
United Kingdom and is the most common unit of measurement in
Canada. In the US and the UK,
personal heights are expressed in feet and inches by people of all ages. In Canada, the trend has been shifting towards metres, as shown on a person's
driver's license.
International inch
In 1958 the
United States and countries of the
Commonwealth of Nations defined the length of the international yard to be 0.9144
metres. Consequently, the international inch is defined to be equal to 25.4 millimetres.
The international standard symbol for inch is
in . In some cases, the inch is denoted by a double prime, which is often approximated by
double quotes, and the
foot by a prime, which is often approximated by an
apostrophe. For example, 6 feet 2 inches is denoted by 6′2?.
Equivalence to other units of length
1 international inch is equal to:
- 1,000 thou
- about 0.08333 feet
- about 0.02778 yards
- 2.54 centimetres
Use of the inch
Even in countries where the
metric system is commonplace, the inch is still sometimes used to refer to
...
screens,
Historical origin
The origin of the inch is disputed. Historically, in different parts of the world and at different points in time, the inch has referred to similar but different standard lengths.
The English word
inch comes from Latin
uncia meaning "one twelfth part" ; the word
ounce has the same origin.
In some other languages, the word for "inch" is similar to or the same as the word for "thumb"; for example,
French:
pouce inch,
pouce thumb;
Italian:
pollice inch,
pollice thumb;
Spanish:
pulgada inch,
pulgar thumb;
Portuguese:
polegada inch,
polegar thumb;
Swedish:
tum inch,
tumme thumb;
Dutch:
duim inch,
duim thumb;
Sanskrit:
Angulam inch,
Anguli Finger.
Given the etymology of the word "inch", it would seem that the inch is a unit derived from the
foot, but this was probably only so in Latin and in Roman times. In English, there are records of fairly precise definitions for the size of an inch , so it seems that the foot was then defined as 12 times this length. For example, the old English
ynche was defined as the width of an average man's thumb at the base of the nail, even including the requirement to calculate the average of a small, a medium, and a large man's measures. To account for the much larger length later called an inch, there are also attempts to link it to the distance between the tip of the thumb and the first joint of the thumb, but this may be speculation.
There are records of the unit being used circa 1000 AD . An Anglo-Saxon unit of length was the barleycorn. After 1066, 3 barleycorn was equal to 1 inch; it is not clear which unit was the base unit and which the derived unit.
One source says that the inch was at one time defined in terms of the yard, itself supposedly defined as the distance between
Henry I of England's nose and his thumb. This is unlikely as Henry was born in 1068.
Prior to the adoption of the international inch , the
United Kingdom and other countries of the
Commonwealth of Nations defined the inch in terms of the
Imperial Standard Yard. The
United States and
Canada each had their own, different, definition of the inch, defined in terms of
metric units. The Canadian inch was defined to be equal to 25.4 millimetres.
Metric or decimal inch
A metric inch is the equivalent of an inch under a proposal for the metrification and unification of the English system of measures. It is now considered to be a strange unit of measurement.
In
Sweden, between 1855 to 1863, the existing Swedish "working inch" was replaced by a "decimal inch" which was one tenth of Swedish foot. Proponents argued that a decimal system simplifies calculations. However, having two different Swedish inch measures proved to be complicated. Between 1878 to 1889 it was agreed to introduce the metric units. However, the decimal inch survived in some building construction trades, and decimal fractions of the foot are still used in
land surveying.
See also
