Customary & Metric Systems of Measurement

Beginning December 23, 1975, the U.S., Metric Conversion Act was signed declaring a national policy of encouraging the voluntary use of the metric system. Federal agencies are in the process of making a transition to the metric system for their business-related activities.

Today the metric system, or SI system (Systeme International d'Unites), exists side by side with the U.S. customary system, which dates back to colonial days but is different from the British Imperial System. The debate on whether the United States should adopt the metric system has been going on for nearly 200 years. Today the United States is the only country in the world not totally committed to adopting the system.

The metric system is often considered a simpler form of measurement in that it includes only seven base units for different types of measurement:

The unit of length is the meter

The unit of mass is the kilogram

The unit of temperature is the kelvin

The unit of time is the second

The unit of electric current is the ampere

The unit of light intensity is the candela

The unit of substance amount is the mole

All other metric units are derived from these units. For example, a newton, the unit of force, involves meters, kilograms, and seconds. A pascal, the unit of pressure, is one newton per square meter. Although the metric system was designed to fill all the needs of scientists and engineers, laypeople need know and use only a few simple parts of it.

The metric system is based on the decimal system and follows a consistent name scheme using prefixes. Multiples and submultiples are always related to powers of 10. For example, deka means ten times, hecto means a hundred times, kilo means a thousand times, mega means a million times, and so on; deci means a tenth of, centi means a hundredth of, milli means a thousandth of, micro means a millionth of, and so on.

Tables of Metric Weights and Measures