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At present in the United States many engineering calculations are made in units of the so-called British Engineering System (BES) whereas "scientific" (physics, chemistry, etc.) work is often carried out and reported in some form of the metric system. Since even in the metric system there is not complete uniformity, a "modernized" metric system, called The International System of Units (abbreviated SI), has been proposed and very likely will ultimately be accepted by all nations. This may take some time in the United States and one must, as an engineer, be prepared to work in both systems. In SI there are six basic units and all others are combinations of these:

Length-meter Mass-kilogram Time-second

Electric current-ampere Thermodynamic temperature-degree Kelvin Light intensity--candela

Note that force is not considered a basic unit; it is defined in terms of mass, length, and time. We will now give a brief listing of the basic units and conversions and a few of the more common derived quantities.