is a unit
a number of different systems. In contemporary English,
most commonly refers to the statute mile
, or 1,609.344 meters
the nautical mile
of 1,852 meters
(6,076.12 ft). There are many other historical miles, and similar
units in other systems translated as miles in English, varying
between one and fifteen kilometers
. It is
about a third of the old measurement, the league
Use of the
mile as a unit of measurement is largely confined to the United States and the United Kingdom where it remains customary.
Elsewhere it has been
replaced by the kilometer as a measure of distance.
There have been several abbreviations for mile (with and without
trailing period): mi
United States, the National
Institute of Standards and Technology now uses and recommends
mi but in everyday usage (at least in the United States and in the United Kingdom) usages such as miles per
hour and miles per gallon are
almost always abbreviated as mph or mpg (rather
than mi/h or mi/gal).
The formula "multiply by 8 and divide by 5" to convert miles to
kilometers gives a conversion of 1.6 kilometers per mile. As it is
about 0.6% lower than the actual conversion factors, it is a useful
approximation for everyday use.
The statute mile
was defined by English Act of Parliament
(hence the name) in
1592, during the reign of Queen
; it is equal to 1,760 yards
, the statute mile is divided
into eight furlongs
; each furlong is ten
; each chain is four rods
(also known as poles
); and each rod is 25 links
. This makes the rod equal to 5½ yards
or 16½ feet in both Imperial and U.S. usage.
The exact conversion of the mile to SI units
depends on which definition of the yard is in use. Different
English-speaking countries maintained independent physical
standards for the yard that were found to differ by small but
measurable amounts, and even to slowly shorten in length. The
United States redefined the U.S. yard in 1893, but this resulted in
U.S. and Imperial units with the same names having very slightly
different values. The difference was resolved in 1959 with the
definition of the international yard in terms of the meter by Australia, Canada, New Zealand, South Africa, the
United Kingdom, and the United States.
mile" of 1,760 international yards is exactly
The difference from the previous standards was 2 ppm
, or about 3.2 millimeters
(1/8 inch) in each mile, the old U.S. standard being slightly
longer and the old Imperial standards slightly shorter than the
international mile. The older standards for the yard (and hence
the foot and the mile) continue in use for some surveying purposes
in the United States. and the old Imperial value of the yard was
used in converting measurements to metric values in India in a 1976
Act of the Indian Parliament.
For most applications, the difference between the two definitions
is insignificant — one international foot is exactly 0.999998 of a
U.S. survey foot, for a difference of about 3.2 millimeters
(1/8 inch) per mile — but it affects the definition of the
State Plane Coordinate
(SPCSs), which can stretch over hundreds of miles. When
international measure was introduced in the English-speaking
countries, the basic geodetic datum
in North America was the North
of 1927 (NAD27), which had been constructed by
based on the definition
of the foot in the Mendenhall Order
of 1893, that is 1 foot = meters: this
definition was retained for data derived from NAD27, but renamed
the U.S. survey foot
to distinguish it from the
The NAD27 was replaced in the 1980s by The North American Datum of
1983 (NAD83), which is defined in meters. The State Plane
Coordinate Systems were also updated, but the National Geodetic Survey
decision of which (if any) definition of the foot to use to the
individual states. All State Plane Coordinate Systems are defined
in meters, but seven states also have State Plane Coordinate
Systems defined in U.S. survey feet and an eighth state in
international feet: the other 42 states use only meter-based
State Plane Coordinate Systems. The current National Topographic
Database of the Survey of India
based on the metric WGS-84 datum
, which is also used by the Global Positioning System
State legislation is also important for determining the conversion
factor to be used for everyday land surveying and real estate
transactions, although the difference (2 ppm
) is of no practical significance given
the precision of normal surveying measurements over short distances
(usually much less than a mile). In the U.S., twenty-four states
have legislated that surveying measures should be based on the U.S.
survey foot, eight have legislated that they be made on the basis
of the international foot, and eighteen have not specified the
conversion factor from metric units.
Historical miles in Britain and Ireland
The statute of Elizabeth I was not the only definition of the
mile in Britain and Ireland. Perhaps the earliest tables of English
linear measures, Arnold's Customs of London
indicates a mile consisted of 8 furlongs, each of
625 feet, for a total of 5,000 feet (1,666⅔ yards,
0.947 statute miles): this is the same definition of the mile
in terms of feet as used by the Romans. The "old English" mile of
medieval and early modern times appears to have measured
approximately 1.3 statute miles.
The Scots mile was longer than the English mile, but varied in
length from place to place. It was formally abolished by an Act of
the Parliament of Scotland
1685, and again by the Treaty of
with England in 1707, but continued in use as a customary
unit during the 18th century. It was obsolete by the time of its
final abolition by the Weights and Measures Act 1824
An estimate of its length can be made from other Scots units
Scots, the rod
was usually called the
, and was
equal to six ells
of 37 inches. As there
are 320 rods in a mile, this would make the Scots mile equal
to 5,920 feet (1,973⅓ yards, 1.12 statute miles). Other
estimates are similar.
The Irish mile was longer still. In Elizabethan times
, four Irish
miles was often equated to five English, though whether the statute
mile or the "old English" mile is unclear. By the seventeenth
century, it was 2,240 yards (6,720 feet,
1.27 statute miles) Again, the difference arose from a
different length of the rod
(usually called the perch
locally): 21 feet as
opposed to 16½ feet in England.
From 1774, through the 1801 union
, until the 1820s, the grand
of 25 Irish counties commissioned surveyed maps at
scales of one or two inches per Irish mile. Scottish engineer
William Bald's County Mayo maps of 1809–30 were drawn in English miles and
rescaled to Irish miles for printing. The Howth–Dublin Post
Office extension of the London–Holyhead turnpike engineered
by Thomas Telford had mileposts in
Although legally abolished by the Weights and
Measures Act 1824, the Irish mile was used till 1856 by the Irish
Post Office. The Ordnance
Survey of Ireland
, from its establishment in 1824, used English
In 1894, Alfred Austin
after visiting Ireland that "the Irish mile is a fine source of
confusion when distances are computed. In one county a mile means a
statute mile, in another it means an Irish mile". When the Oxford English Dictionary
definition of "mile" was published in 1906, it described the Irish
mile as "still in rustic use". A 1902 guide says regarding milestones, "Counties Dublin, Waterford, Cork, Antrim, Down,
English, but Donegal Irish Miles
; the other counties
either have both, or only one or two
roads have Irish". Variation in signage persisted till the
publication of standardised road traffic regulations by the
Irish Free State
in 1926. In 1937,
a man prosecuted for driving outside the 15-mile limit of his
license offered the unsuccessful defense that, since the state was
independent, the limit ought to use Irish miles, "just as no one
would ever think of selling land other than as Irish acre
". A 1965 proposal by two TD
, to replace statute miles with Irish
miles in a clause of the Road Transport Act, was rejected. The term
is now obsolete as a specific measure, though an "Irish mile"
colloquially is a long but vague distance akin to a "country mile".
Outside of its downtown core, but within its newer subdivisions,
Toronto' street grid is based on the Irish mile.
The term metric mile
is used in sports
such as athletics
to denote a distance of
(about 4,921 ft). In
United States high school competition, the term is sometimes used
for a race of 1,600 meters (about 5,249 ft).
The nautical mile
was originally defined as one
minute of arc
along a meridian
of the Earth. It is a
convenient reference since it is fairly constant at all latitudes,
in contrast with degrees of longitude which vary from 60 NM at
the equator to zero at the poles.
Navigators use dividers to step off the distance between two points
on the navigational chart, then place the open dividers against the
minutes-of-latitude scale at the edge of the chart, and read off
the distance in nautical miles. Since it is now known that the
Earth is not perfectly spherical but an oblate spheroid, the length
derived from this method varies slightly from the equator to the
poles. For instance, using the WGS84 Ellipsoid
, the commonly accepted
Earth model for many purposes today, one minute of latitude at the
WGS84 equator is 6,087 feet and at the poles is 6,067 feet. On
average it is about 6,076 feet (about 1852 meters
or 1.15 statute
of America, the nautical mile was defined in the nineteenth
century as 6,080.2 feet (1,853.249 m), whereas in the
Kingdom the Admiralty nautical mile was
defined as 6,080 feet (1,853.184 m) and was approximately
one minute of latitude in the latitudes of the south of the
Other nations had different definitions of the nautical
mile, but it is now internationally defined to be exactly
Related nautical units
The nautical mile per hour is known as the knot
. Nautical miles and knots are almost
universally used for aeronautical and maritime navigation because
of their relationship with degrees and minutes of latitude and the
convenience of using the latitude scale on a map for distance
The data mile
is used in radar
-related subjects and is equal to 6,000 feet
). The radar
is a unit of time (in the same way that the light year
is a unit of distance), equal to the
time required for a radar pulse to travel a distance of two miles
(one mile each way). Thus, the radar statute mile is 10.8 μs
and the radar nautical mile is 12.4 μs.
In Roman times, the unit of long distance (literally "a thousand
" in Latin
, with one
pace being equal to two steps) was first used by the Romans
and denoted a distance of
1,000 paces or 5,000 Roman feet, and is estimated to
correspond to about 1,479 meters (1,617 yards). This unit
is now known as the Roman mile
. This unit spread
throughout the Roman empire, often with modifications to fit local
systems of measurements.
in the continental United States often
laid out by miles. Detroit, Indianapolis, Chicago, Phoenix, Philadelphia, Las Vegas, Los
Angeles and Miami are several
Typically the largest streets are about one mile
apart, with others at half-mile, quarter-mile intervals.
Manhattan (New York) "streets" are almost exactly 20 per
mile, while "avenues" are about six per mile.
- The Arab mile (or Arabic mile) was a
unit of length used by medieval Muslim geographers. Its precise
length is uncertain, but believed to be around 1925 meters.
- The Danish (traditional) was 24,000 Danish feet or 7532.5
meters. Sometimes it was interpreted as exactly 7.5 kilometers. It
is the same as the north German (below).
- The was a traditional unit in German speaking countries, much
longer than a western European mile. It was 24,000 German feet; the
SI equivalent was 7586 meters in Austria or 7532.5 meters in
northern Germany. There was a version known as the which was 4
Admiralty nautical miles, 7,412.7 meters, or 1/15 degree.
- In Norway and Sweden a mil is a unit
of length which is equal to 10 kilometers and commonly used in
everyday language. However in more formal situations, like on road
signs and when there is risk of confusion with English miles,
kilometers are used instead. The traditional Swedish spanned the
range from 6000-14,485 meters, depending on province. It was however standardized in
1649 to 36,000 Swedish feet, or 10.687 kilometers. The Norwegian
was 11.298 kilometers. When the metric system was introduced in the
union in 1889, one standardized the to exactly 10
- The Russian was a traditional Russian
unit of distance, equal to 7 verst, or 7.468 km
- The (Croatian mile) is 11,130 meters = 11.13 kilometers = 1/10
of equator's degree., first time used by Jesuit Stjepan
Glavač on map from 1673.
- The (also called ) (mile of Croatian Ban, Croatian mile) was 7586 meters =
7.586 kilometers, or 24,000 feet..
Even in countries that have moved from the Imperial
to the Metric system
(for example, Australia and New
Zealand), the mile is still used in a variety of idioms
. These include:
- A country mile is
used colloquially to denote a very long
- "An inch is as good as a mile" (failure by a narrow
margin is no better than any other failure)
- "Give him an inch and he'll take a mile" (the person
in question will become greedy if shown generosity)
- "Missed by a mile" (missed by a wide margin)
- "Talk a mile a minute" (speak at a rapid rate)
- "To go the extra mile" (to put in extra effort)
- "Miles away" (lost in thought, or daydreaming)
- "Milestone" (an event
indicating significant progress)
- Tina Butcher et al. ed. (2007) Appendix C, p. C-13.
- Klein (1974, corrected 1988), p. 69.
- Barbrow & Judson, (1976), pp. 16, 17, 20.
- Astin, A. V., Karo, H. A.; Mueller, F. H. (June 25, 1959). "
Refinement of Values for the Yard and the
Pound." Federal Register Doc. 59-5442.
When reading the document it helps to bear in mind that 999,998 =
3,937 × 254.
- Schedule to the Standards of Weights and Measures Act,
of India, " National Map Policy – 2005".
- " Act for a standard of miles" (June 16, 1685).
APS viii: 494, c.59. RPS
- Union with England Act 1707 (c. 7),
- Rowlett (2005). s.v. mile.
- Maloney, (1978), 34.
- Maloney, (1978), 34–35.
- Rowlett (2005). s.v. data mile.
- Rowlett (2005). s.v. radar mile.
- Smith (1875), p. 171.
- Rowlett (2005). s.v. mil .
- Rowlett (2005), s.v meile.
- Centuries of Natural Science in Croatia : Theory
and Application Kartografija i putopisi
- Vijenac Mrvice s banskoga stola
Heritage Dictionary of the English Language (3rd ed.)
(1992). Boston: Houghton Mifflin Company.
- Astin. V. and H. Arnold Karo. (1959). Refinement of values for the yard and the
pound, Washington DC: National Bureau of Standards,
republished on National Geodetic Survey web site and the Federal
Register (Doc. 59-5442, Filed, June 30, 1959, 8:45 a.m.)
- Barbrow, Louis E. and Lewis V. Judson (1976). Weights
and Measures Standards of the United States: a brief
Institute of Standards and Technology.
- Butcher, Tina et al. ed. (2007). NIST Handbook 44: Specifications, Tolerances, and
Other Technical Requirements for Weighing and Measuring
Devices. Appendix C, p. C-13.
- Klein, Herbert Arthur (1974, corrected 1988). The Science
of Measurement: A Historical Survey. New York: Dover.
(previously published by Simon & Schuster under the title
The World of Measurements: Masterpieces, Mysteries and Muddles
- Maloney, Elbert S. (1978). Dutton's Navigation and
Piloting. 13th Ed. Annapolis: Naval Institute Press.
- Rowlett, Russ (2005). How Many? A Dictionary of Units of Measurement.
member's web page at University of North Carolina at Chapel
Hill. Accessed 2007-11-10.
- Thompson, Ambler, and Taylor, Barry. (2008). Guide for the Use of the International System of Units
(SI) (Special Publication 811). Gaithersburg, MD: National
Institute of Standards and Technology.