As of Version 9.0, unit functionality is built into the Wolfram Language

Units Package

There are many systems of units. The particular set of units that is used depends on factors as various as the field of study and the author's country of origin. The function Convert provides conversion between different units.

Convert[old,newunits]convert old to a form involving a combination of newunits

Converting units.

This loads the package.
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This converts meters per second into miles per hour.
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You have to give prefixes for units as separate words.
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The conversion of temperature units is different from most other unit conversions because it is not multiplicative. This is simply because the zeros of various systems are set at different values. For example, zero degrees Centigrade is the same as 32 degrees Fahrenheit.

ConvertTemperature[temp,oldunits,newunits] convert temp from the oldunits scale to the newunits scale

Converting temperatures.

This converts the temperature. Convert only converts units of temperature.
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Temperature scales.

To organize the use of units, certain standardized systems have been developed. These include the International System (SI) and systems using particular metric units, such as the meter/kilogram/second system. The functions SI, MKS, and CGS convert various units into the standard systems.

SI[expr] convert expr to SI units (International System)
MKS[expr] convert expr to MKS units (meter/kilogram/second)
CGS[expr] convert expr to CGS units (centimeter/gram/second)

Conversion of units into standard systems.

The International Standard unit for pressure is the pascal.
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You can request information about any unit.

SI unit prefixes.

Electrical units.

Units of length.

Units of information.

Units of time.

Units of mass.

Units of weight.

Units of force.

Units of inverse length.

Units of volume.

Units of viscosity.

Units of types of luminous energy and intensity.

Units of radiation.


Units of power.

Units of area.

Amounts of substances.

Acceleration due to gravity.

Magnetic units.

Unit multipliers.

Units of pressure.

Units of energy.

Unit of frequency.

Unit of speed.

Unit of fineness for yarn or thread.