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.

${\frac {5{\cancel {\text{km}}}}{\text{s}}}\cdot$${\frac {{1000}{\text{ m}}}{{1}{\cancel {\text{ km}}}}}$$=$${\frac {5000\cdot {\text{m}}}{{\text{s}}\cdot {1}}}=$${\frac {5000{\text{ m}}}{\text{s}}}$

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 GNU units for Linux and Windows.

Tables of conversion factors

Area

Name of unit	Symbol	Definition	Relation to SI units
acre (international)	ac	≡ Template:Nowrap = Template:Val	≡ Template:Val
acre (US survey)	ac	≡ 10 sq ch = Template:Val, also Template:Val	≈ Template:Val
are	a	≡ 100 m2	≡ 100 m2
barn	b	≡ 10−28 m2	≡ 10−28 m2
barony		≡ Template:Val ac	≡ Template:Val
board	bd	≡ Template:Nowrap	≡ Template:Val
boiler horsepower equivalent direct radiation	bhp EDR	≡ 1 ft2 × 1 bhp / (240 BTUIT/h)	≈ Template:Val
circular inch	circ in	≡ Template:Frac sq in	≈ Template:Val
circular mil; circular thou	circ mil	≡ Template:Frac mil2	≈ Template:Val
cord		≡ 192 bd	≡ Template:Val
cuerda (PR Survey)	cda	≡ 1 cda x 1 cda = Template:Val acre	≡ Template:Val
dunam		≡ Template:Val	≡ Template:Val
guntha (India)		≡ 121 sq yd	≈ 101.17 m2
hectare	ha	≡ Template:Val	≡ Template:Val
hide		≈ 120 ac (variable)	≈ Template:Val
rood	ro	≡ Template:Frac ac	= Template:Val
ping		≡ Template:Frac m × Template:Frac m	≈ Template:Val
section		≡ 1 mi × 1 mi	= Template:Val
shed		≡ 10−52 m2	= 10−52 m2
square (roofing)		≡ 10 ft × 10 ft	= Template:Val
square chain (international)	sq ch	≡ 66 ft × 66 ft = Template:Frac ac	≡ Template:Val
square chain (US Survey)	sq ch	≡ 66 ft (US) × 66 ft (US) = Template:Frac US survey acre	≈ Template:Val
square foot	sq ft	≡ Template:Nowrap	≡ Template:Val
square foot (US Survey)	sq ft	≡ Template:Nowrap	≈ Template:Val
square inch	sq in	≡ Template:Nowrap	≡ Template:Val
square kilometre	km2	≡ 1 km × 1 km	= 106 m2
square link (Gunter's)(International)	sq lnk	≡ 1 lnk × 1 lnk ≡ 0.66 ft × 0.66 ft	= Template:Val
square link (Gunter's)(US Survey)	sq lnk	≡ Template:Nowrap ≡ Template:Nowrap	≈ Template:Val
square link (Ramsden's)	sq lnk	≡ 1 lnk × 1 lnk ≡ 1 ft × 1 ft	= Template:Val
square metre (SI unit)	m2	≡ 1 m × 1 m	= 1 m2
square mil; square thou	sq mil	≡ 1 mil × 1 mil	= Template:Val
square mile	sq mi	≡ 1 mi × 1 mi	≡ Template:Val
square mile (US Survey)	sq mi	≡ 1 mi (US) × 1 mi (US)	≈ Template:Val
square rod/pole/perch	sq rd	≡ 1 rd × 1 rd	= Template:Val
square yard (International)	sq yd	≡ 1 yd × 1 yd	≡ Template:Val
stremma		≡ Template:Val	= Template:Val
township		≡ 36 sq mi (US)	≈ Template:Val
yardland		≈ 30 ac	≈ Template:Val

Licensing

Content obtained and/or adapted from:

• Conversion of units, Wikipedia under a CC BY-SA license