Units CGS-SI Interconversions

From time to time, probably all science students find themselves entangled in a problem of units. For those who have advanced through physical chemistry to the level of this book, these problems have obviously not been insurmountable. It is likely, however, that —along with feelings of frustration—these students have been left with the wish that everyone used the same units, specifically those units with which they are most comfortable. In response to the recognized need for uniformity, IUPAC recommends the use of Systeme international d unites (International System of Units, SI) units, which are essentially standardized mks units. 

The SI system is based on mutually consistent units assigned to the nine physical quantities listed in Table B. 1. In addition to the SI units for these nine quantities, the table also lists cgs or other commonly encountered units, as well as the conversion factors between the two. In this table the headings at the top of the table indicate how the conversion factors are to be used in going from SI to cgs/common units, whereas the bottom headings indicate the use of these factors for calculations in the reverse direction. 

From these nine basic quantities, numerous other SI units may be derived. Table B.2 lists a number of these derived units, particularly those relevant to colloid and surface chemistry. The table is arranged alphabetically according to the name of the physical quantity involved. Note that instructions for the use of the conversion factors —depending on the direction of the conversion —are given in the top and bottom headings of the columns. Table B.2 is by no means an exhaustive list of the various derived SI units Hopkins (1973) reports on many additional conversions, as do most handbooks and numerous other references. 

One reason for the great diversity of units in existence is the fact that quantities of such diverse magnitudes are measured. A general rule is that the unit should be appropriate in magnitude to the quantity being measured. To obtain a dimension of convenient size in SI units, the SI unit is multiplied by a power of 10 and the prefixes listed in Table B.3 are affixed to the unit. 

Hopkins, R. A., The International (SI) Metric System and How It Works, Polymeric Services, Reseda, CA, 1973. 

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