View source for Measurement (AREA) – CONVERSION

==Techniques==

=== Process overview ===

The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards. Engineering judgment may include such factors as:
* The precision and accuracy of measurement and the associated uncertainty of measurement.
* The statistical confidence interval or tolerance interval of the initial measurement.
* The number of significant figures of the measurement.
* The intended use of the measurement including the engineering tolerances.
* Historical definitions of the units and their derivatives used in old measurements; e.g., international foot vs. US survey foot.

Some conversions from one system of units to another need to be exact, without increasing or decreasing the precision of the first measurement. This is sometimes called ''soft conversion''. It does not involve changing the physical configuration of the item being measured.

By contrast, a ''hard conversion'' or an ''adaptive conversion'' may not be exactly equivalent. It changes the measurement to convenient and workable numbers and units in the new system. It sometimes involves a slightly different configuration, or size substitution, of the item. Nominal values are sometimes allowed and used.

=== Conversion factors ===
A conversion factor is used to change the units of a measured quantity without changing its value. The '''unity bracket method''' of unit conversion consists of a fraction in which the denominator is equal to the numerator, but they are in different units. Because of the identity property of multiplication, the value of a quantity will not change as long as it is multiplied by one. Also, if the numerator and denominator of a fraction are equal to each other, then the fraction is equal to one. So as long as the numerator and denominator of the fraction are equivalent, they will not affect the value of the measured quantity.

The following example demonstrates how the unity bracket method is used to convert the rate 5 kilometers per second to meters per second. The symbols km, m, and s represent kilometer, meter, and second, respectively.

<math>\frac{5 \cancel {\text {km}}}{\text {s}}
\cdot</math><math>\frac{{1000 }\text { m}}{{1}{\cancel {\text { km}}}}</math><math>=</math><math>\frac{{5000 \cdot {\text {m}}}}{{\text {s}\cdot {1}}}
=</math><math>\frac {5000{\text { m}}}{\text {s}}</math>

Thus, it is found that 5 kilometers per second is equal to 5000 meters per second.

=== Software tools ===
There are many conversion tools. They are found in the function libraries of applications such as spreadsheets databases, in calculators, and in macro packages and plugins for many other applications such as the mathematical, scientific and technical applications.

There are many standalone applications that offer the thousands of the various units with conversions. For example, the free software movement offers a command line utility [https://www.gnu.org/software/units/ GNU units] for Linux and Windows.

== Tables of conversion factors ==

{| class="wikitable"
|+ Area
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-
| acre (international) || ac
| ≡ 1 ch × 10 ch = 4840 sq yd
| ≡ 4 046.856 4224 m<sup>2</sup>
|-
| acre (US survey) || ac
| ≡ 10 sq ch = 4840 sq yd, also 43 560 sq ft
| ≈ 4 046.873 m<sup>2</sup>
|-
| are || a
| ≡ 100&nbsp;m<sup>2</sup>
| ≡ 100&nbsp;m<sup>2</sup>
|-
| barn || b
| ≡ 10<sup>−28</sup>&nbsp;m<sup>2</sup>
| ≡ 10<sup>−28</sup>&nbsp;m<sup>2</sup>
|-
| barony || &nbsp;
| ≡ 4000 ac
| ≡ 1.618 742 568 96 x 10<sup>7</sup> m<sup>2</sup>
|-
| board || bd
| ≡ 1 in × 1 ft
| ≡ 7.741 92 x 10<sup>-3</sup> m<sup>2</sup>
|-
| boiler horsepower equivalent direct radiation || bhp EDR
| ≡ 1&nbsp;ft<sup>2</sup> × 1&nbsp;bhp / (240&nbsp;BTU<sub>IT</sub>/h)
| ≈ 12.958 174 m<sup>2</sup>
|-
| circular inch || circ in
| ≡ <math> \tfrac{\pi}{4}</math> sq in
| ≈ 5.067 075 x 10<sup>-4</sup> m<sup>2</sup>
|-
| circular mil; circular thou || circ mil
| ≡ <math> \tfrac{\pi}{4}</math> &nbsp;mil<sup>2</sup>
| ≈ 5.067 075 x 10<sup>-10</sup> m<sup>2</sup>
|-
| cord || &nbsp;
| ≡ 192&nbsp;bd
| ≡ 1.486 448 64 m<sup>2</sup>
|-
| cuerda (PR Survey) || cda
| ≡ 1 cda x 1 cda = 0.971 222 acre
| ≡ 3 930.395 625 m<sup>2</sup>
|-
| dunam || &nbsp;
| ≡ 1000 m<sup>2</sup>
| ≡ 1000 m<sup>2</sup>
|-
| guntha (India) || &nbsp;
| ≡ 121&nbsp;sq&nbsp;yd
| ≈ 101.17&nbsp;m<sup>2</sup>
|-
| hectare || ha
| ≡ 10 000 m<sup>2</sup>
| ≡ 10 000 m<sup>2</sup>
|-
| hide || &nbsp;
| ≈ 120 ac (variable)
| ≈ 5 x 10<sup>5</sup> m<sup>2</sup>
|-
| rood || ro
| ≡ <math> \tfrac{1}{4}</math>&nbsp;ac
| = 1 011.714 1056 m<sup>2</sup>
|-
| ping ||
| ≡ <math> \tfrac{20}{11}</math>&nbsp;m × <math> \tfrac{20}{11}</math>&nbsp;m
| ≈ 3.306 m<sup>2</sup>
|-
| section ||
| ≡ 1 mi × 1 mi
| = 2.589 988 110 336 x 10<sup>6</sup> m<sup>2</sup>
|-
| shed || &nbsp;
| ≡ 10<sup>−52</sup>&nbsp;m<sup>2</sup>
| = 10<sup>−52</sup>&nbsp;m<sup>2</sup>
|-
| square (roofing) ||
| ≡ 10 ft × 10 ft
| = 9.290 304 m<sup>2</sup>
|-
| square chain (international) || sq ch
| ≡ 66 ft × 66 ft = <math> \tfrac{1}{10}</math> ac
| ≡ 404.685 642 24 m<sup>2</sup>
|-
| square chain (US Survey) || sq ch
| ≡ 66 ft (US) × 66 ft (US) = <math> \tfrac{1}{10}</math> US survey acre
| ≈ 404.6873 m<sup>2</sup>
|-
| square foot || sq ft
| ≡ 1 ft × 1 ft
| ≡ 9.290 304 x 10<sup>-2</sup> m<sup>2</sup>
|-
| square foot (US Survey) || sq ft
| ≡ 1 ft (US) × 1 ft (US)
| ≈ 9.290 341 161 3275 x 10<sup>-2</sup> m<sup>2</sup>
|-
| square inch || sq in
| ≡ 1 in × 1 in
| ≡ 6.4516 x 10<sup>-4</sup> m<sup>2</sup>
|-
| square kilometre || km<sup>2</sup>
| ≡ 1&nbsp;km × 1&nbsp;km
| = 10<sup>6</sup> m<sup>2</sup>
|-
| square link (Gunter's)(International) || sq lnk
| ≡ 1 lnk × 1 lnk ≡ 0.66&nbsp;ft × 0.66&nbsp;ft
| = 4.046 856 4224 x 10<sup>-2</sup> m<sup>2</sup>
|-
| square link (Gunter's)(US Survey) || sq lnk
| ≡ 1 lnk × 1 lnk ≡ 0.66 ft (US) × 0.66 ft (US)
| ≈ 4.046 872 x 10<sup>-2</sup> m<sup>2</sup>
|-
| square link (Ramsden's) || sq lnk
| ≡ 1 lnk × 1 lnk ≡ 1&nbsp;ft × 1&nbsp;ft
| = 0.092 903 04 m<sup>2</sup>
|- style="background:#dfd;"
| square metre (SI&nbsp;unit) || m<sup>2</sup>
| ≡ 1 m × 1 m
| = 1 m<sup>2</sup>
|-
| square mil; square thou || sq mil
| ≡ 1 mil × 1 mil
| = 6.4516 x 10<sup>-10</sup> m<sup>2</sup>
|-
| square mile || sq mi
| ≡ 1&nbsp;mi × 1&nbsp;mi
| ≡ 2.589 988 110 336 x 10<sup>6</sup> m<sup>2</sup>
|-
| square mile (US Survey) || sq mi
| ≡ 1&nbsp;mi (US) × 1&nbsp;mi (US)
| ≈ 2.589 998 47 x 10<sup>6</sup> m<sup>2</sup>
|-
| square rod/pole/perch || sq rd
| ≡ 1 rd × 1 rd
| = 25.292 852 64 m<sup>2</sup>
|-
| square yard (International) || sq yd
| ≡ 1 yd × 1 yd
| ≡ 0.836 127 36 m<sup>2</sup>
|-
| stremma || &nbsp;
| ≡ 1000 m<sup>2</sup>
| = 1000 m<sup>2</sup>
|-
| township || &nbsp;
| ≡ 36 sq mi (US)
| ≈ 9.323 994 x 10<sup>7</sup> m<sup>2</sup>
|-
| yardland || &nbsp;
| ≈ 30 ac
| ≈ 1.2 x 10<sup>5</sup> m<sup>2</sup>
|}

== Licensing ==
Content obtained and/or adapted from:
* [https://en.wikipedia.org/wiki/Conversion_of_units Conversion of units, Wikipedia] under a CC BY-SA license