The ConvUtils unit declares a general-purpose Conversion Function that you can use to convert a measurement from one set of units to another. You can perform conversions between compatible units of measurement such as feet and inches or days and weeks. Units that measure the same types of things are said to be in the same conversion family. The units you're converting must be in the same conversion family. For information on doing conversions, see Performing Conversions. 

The StdConvs unit defines several conversion families and measurement units within each family. In addition, you can create customized conversion families and associated units using the RegisterConversionTypeand RegisterConversionFamily functions. For information on extending conversion and conversion units, see Adding new measurement types.