Measurement (AREA) – CONVERSION
Contents
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.
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
| Name of unit | Symbol | Definition | Relation to SI units |
|---|---|---|---|
| acre (international) | ac | ≡ 1 ch × 10 ch = 4840 sq yd | ≡ 4 046.856 4224 m2 |
| acre (US survey) | ac | ≡ 10 sq ch = 4840 sq yd, also 43 560 sq ft | ≈ 4 046.873 m2 |
| are | a | ≡ 100 m2 | ≡ 100 m2 |
| barn | b | ≡ 10−28 m2 | ≡ 10−28 m2 |
| barony | ≡ 4000 ac | ≡ 1.618 742 568 96 x 107 m2 | |
| board | bd | ≡ 1 in × 1 ft | ≡ 7.741 92 x 10-3 m2 |
| boiler horsepower equivalent direct radiation | bhp EDR | ≡ 1 ft2 × 1 bhp / (240 BTUIT/h) | ≈ 12.958 174 m2 |
| 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 | ≡ 1 ft (US) × 1 ft (US) | ≈ Template:Val |
| square inch | sq in | ≡ 1 in × 1 in | ≡ 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 | ≡ 1 lnk × 1 lnk ≡ 0.66 ft (US) × 0.66 ft (US) | ≈ 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
