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The **square mile** (abbreviated as **sq mi** and sometimes as **mi²**)^{ [1] } is an imperial and US unit of measure for an area equal to the area of a square with a side length of one statute mile.^{ [2] } It should not be confused with *miles square*, which refers to a square region with each side having the specified length. For instance, 20 miles square (20 × 20 miles) has an area equal to 400 square miles; a rectangle of 10 × 40 miles likewise has an area of 400 square miles, but it is not 20 miles square.

**Area** is the quantity that expresses the extent of a two-dimensional figure or shape, or planar lamina, in the plane. Surface area is its analog on the two-dimensional surface of a three-dimensional object. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat. It is the two-dimensional analog of the length of a curve or the volume of a solid.

The **mile** is an English unit of length of linear measure equal to 5,280 feet, or 1,760 yards, and standardised as exactly 1,609.344 metres by international agreement in 1959.

One square mile is equal to:

- 4,014,489,600 square inches
^{ [3] } - 27,878,400 square feet
^{ [3] } - 3,097,600 square yards
^{ [3] } - 640 acres
^{ [1] } - 2560 roods
^{ [4] }

A **square inch** is a unit of area, equal to the area of a square with sides of one inch. The following symbols are used to denote square inches:

The **square foot** is an imperial unit and U.S. customary unit of area, used mainly in the United States and partially in Bangladesh, Canada, Ghana, Hong Kong, India, Malaysia, Nepal, Pakistan, Singapore and the United Kingdom. It is defined as the area of a square with sides of 1 foot.

The **square yard** is an imperial unit of area, formerly used in most of the English-speaking world but now generally replaced by the square metre, however it is still in widespread use in the U.S., Canada, the U.K. and India. It is defined as the area of a square with sides of one yard in length.

Since one inch has been standardized to 2.54 cm by international agreement, a square mile is equivalent to the following metric measures:

The **metric system** is an internationally recognised decimalised system of measurement. It is in widespread use, and where it is adopted, it is the only or most common system of weights and measures. It is now known as the International System of Units (SI). It is used to measure everyday things such as the mass of a sack of flour, the height of a person, the speed of a car, and the volume of fuel in its tank. It is also used in science, industry and trade.

- 25,899,881,103.36 square centimetres
- 2,589,988.110336 square metres
- 258.9988110336 hectares
- 2.589988110336 square kilometres

The **square metre** or **square meter** is the SI derived unit of area with symbol **m ^{2}**.

The **hectare** is an SI accepted metric system unit of area equal to a square with 100-metre sides, or 10,000 m^{2}, and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. An acre is about 0.405 hectare and one hectare contains about 2.47 acres.

**Square kilometre** or **square kilometer**, symbol **km ^{2}**, is a multiple of the square metre, the SI unit of area or surface area.

When applied to a portion of the earth's surface, "square mile" is an informal synonym for section.

In U.S. land surveying under the Public Land Survey System (PLSS), a **section** is an area nominally one square mile, containing 640 acres, with 36 sections making up one survey township on a rectangular grid.

Romans derived measurements from marching. Five feet was equal to one pace (which is appropriately a double step). One thousand paces measured a Roman mile, which was somewhat smaller than the English statute mile. This Roman system was adopted, with local variations, throughout Europe as the Roman Empire spread.^{ [5] }

Total population in a square mile is derived by dividing the total number of residents by the number of square miles of land area in the specified geographic area. The population per square kilometer is derived by multiplying the population per square mile by 0.3861.^{ [6] }

Land area measurements are originally recorded as whole square meters. Square meters are converted to square kilometers by dividing by 1,000,000; square kilometers are converted to square miles by dividing by 2.58999; square meters are converted to square miles by dividing by 2,589,988.^{ [6] }

The **acre** is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong, which is exactly equal to 10 square chains, ^{1}⁄_{640} of a square mile, or 43,560 square feet, and approximately 4,047 m^{2}, or about 40% of a hectare. Based upon the International yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 square metres. The acre is a statute measure in the United States and was formerly one in the United Kingdom and almost all countries of the former British Empire, although informal use continues.

A **minute of arc**, **arcminute** (arcmin), **arc minute**, or **minute arc** is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn – it is for this reason that the Earth's circumference is almost exactly 21,600 nautical miles. A minute of arc is π/10800 of a radian.

A **furlong** is a measure of distance in imperial units and U.S. customary units equal to one eighth of a mile, equivalent to 660 feet, 220 yards, 40 rods, or 10 chains.

The system of **imperial units** or the **imperial system** is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced. The Imperial units replaced the Winchester Standards, which were in effect from 1588 to 1825. The system came into official use across the British Empire. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement, although some imperial units are still used in the United Kingdom, Canada and other countries formerly part of the British Empire. The imperial system developed from what were first known as English units, as did the related system of United States customary units.

**Length** is a measure of distance. In the International System of Quantities, length is any quantity with dimension distance. In most systems of measurement, the unit of length is a base unit, from which other units are derived.

**United States customary units** are a system of measurements commonly used in the United States. The **United States customary system** developed from English units which were in use in the British Empire before the U.S. became an independent country. However, the United Kingdom's system of measures was overhauled in 1824 to create the imperial system, changing the definitions of some units. Therefore, while many U.S. units are essentially similar to their Imperial counterparts, there are significant differences between the systems.

The **yard** is an English unit of length, in both the British imperial and US customary systems of measurement, that comprises 3 feet or 36 inches.

The **foot** is a unit of length in the imperial and US customary systems of measurement. Since the International Yard and Pound Agreement of 1959, one foot is defined as 0.3048 meter exactly. In customary units, the foot comprises 12 inches and three feet compose a yard.

The **quart** is an English unit of volume equal to a quarter gallon. It is divided into two pints or four cups. Historically, the exact size of the quart has varied with the different values of gallons over time and in reference to different commodities. Presently, three kinds of quarts remain in use: the **liquid quart** and **dry quart** of the US customary system and the **imperial quart** of the British imperial system. All are roughly equal to one metric litre.

The **rod** or **perch** or **pole** is a surveyor’s tool and unit of length exactly equal to 5 ^{1}⁄_{2} yards, 16^{1}⁄_{2} feet, ^{1}⁄_{320} of a statute mile or one-fourth of a surveyor's chain. The rod is useful as a unit of length because whole number multiples of it can form one acre of square measure. The 'perfect acre' is a rectangular area of 43,560 square feet, bounded by sides of length 660 feet and 66 feet or, equivalently, 40 rods and 4 rods. An acre is therefore 160 square rods.

A **league** is a unit of length. It was common in Europe and Latin America, but is no longer an official unit in any nation. The word originally meant the distance a person could walk in an hour. Since the Middle Ages, many values have been specified in several countries.

The **li**, also known as the **Chinese mile**, is a traditional Chinese unit of distance. The li has varied considerably over time but was usually about one third of an English mile and now has a standardized length of a half-kilometer. This is then divided into 1,500 chi or "Chinese feet".

A **pace** is a unit of length consisting either of one normal walking step, or of a double step, returning to the same foot. Like other traditional measurements, paces started as informal units but have since been standardized, often with the specific length set according to a typical brisk or military marching stride.

**English units** are the units of measurement that were used in England up to 1826, which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.

There are a number of **Spanish units of measurement** of length or area that are now virtually obsolete. They include the **vara**, the **cordel**, the **league** and the **labor**. The units of area used to express the area of land are still encountered in some transactions in land today. For example, the 'vara' is still used in Costa Rica when ordering lumber.

**Taiwanese units of measurement** are the customary and traditional units of measure used in Taiwan. The Taiwanese units formed in the 1900s when Taiwan was under Japanese rule. The system mainly refers to Japanese system with some units derived from the Qing era Chinese units and Dutch era Dutch units. The Taiwanese units are pronounced in Taiwanese Hokkien and Hakka before the World War II and adopted by the Mandarin speaking immigrants from China in 1949. Today, the Taiwanese units are used exclusively, in some cases alongside official metric (SI) units, and in other cases they have been supplanted by metric units. Linguistically, practically all Taiwanese units of measure are Chinese classifiers used to classify nouns.

A **coherent system of units** is a system of units based on a system of quantities in such a way that the equations between the numerical values expressed in the units of the system have exactly the same form, including numerical factors, as the corresponding equations between the quantities. Equivalently, it is a system in which every quantity has a unique unit, or one that does not use conversion factors.

The **History of measurement systems in Pakistan** begins in early Indus Valley Civilization when pastoral societies used barter to exchange goods or services and needed units of measurement.

- 1 2 Rowlett, Russ (September 1, 2004). "S",
*How Many? A Dictionary of Units of Measurement*. University of North Carolina at Chapel Hill. Retrieved February 22, 2012. - ↑ Davies, Charles (1872).
*Mathematical dictionary and cyclopedia of mathematical science*. Original from Harvard University: A.S. Barnes and co. p. 582. - 1 2 3 François Cardarelli (2003).
*Encyclopaedia of scientific units, weights, and measures: their SI equivalences and origins*. Springer. p. 3. ISBN 978-1-85233-682-0 . Retrieved 22 February 2012. - ↑ Zupko, Ronald Edward (1985).
*A dictionary of weights and measures for the British Isles: the Middle Ages to the twentieth century*. American Philosophical Society. p. 353. ISBN 978-0-87169-168-2 . Retrieved 22 February 2012. - ↑ "The history of measurement" . Retrieved 9 August 2015.
- 1 2 "Land Area and Persons Per Square Mile".
*Census.gov*. Retrieved 9 August 2015.^{[ permanent dead link ]}

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