Conversion of units

Conversion of units refers to conversion factors between different units of measurement for the same quantity.

Dimensioned values
Carrying units through a mathematical operation is sometimes performed.

e.g. to convert 6 feet into metres. From below one foot is exactly 0.3048 metre. Thus:
 * 6 ft × 0.3048 m/ft = 1.8288 m

This leaves only metres, the desired result.

This works because the numerator and denominator describe the same quantity, the factor is equivalent to the number 1. Therefore, multiplication by this factor does not change the measured quantity, only its units.

Rounding of results
The process of making a conversion cannot produce a more precise result than the original quoted figure. Appropriate rounding of results is normally performed after conversion. (See significant figures).

In the above example the 0.3048 metre per foot is precise by definition, but the precision of the answer is determined by the precision of the 6 ft figure and in many cases the result would need rounding perhaps to 1.8 m.

Mass
Note: see Weight for detail of mass/weight distinction and conversion In physics, the pound of mass is sometimes written lbm to distinguish it from the pound-force (lbf). It should not be read as the mongrel unit "pound metre".

Speed or velocity
A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.

Force
See also: Conversion between weight (force) and mass

Energy
Subscript textSuperscript text===Power===

Information entropy
Often, information entropy is measured in shannons, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning. Other times the bit is used as a measure of information entropy and is thus a synonym of shannon.

Temperature
Note: see Temperature conversion for more detail

Software tools
Home and office computers come with converters in bundled spreadsheet applications or can access free converters via the Internet. Units and measurements can be easily converted using these tools, but only if the units are explicitly defined and the conversion is compatible (e.g., cmHg to kPa).

Free conversion software

 * Units (Unix program) — a popular command-line utility.

General commercial sources of converters

 * Advanced electronic calculators have unit-conversion functionality.
 * Spreadsheet programs usually provide conversion functions or formulas or the user can write their own.
 * Commercial mathematical, scientific and technical applications often include converters.