There are two generally accepted methods of weighing and measuring in the United States. The one most
familiar to Americans is the Foot-Pound or English System. This system has developed over the centuries
and was originally based on royal decrees or ancient Roman custom. As an example, the mile was
based on 1,000 Roman paces, with each pace equal to five feet. (England’s Queen Elizabeth I changed
the definition to 5,280 feet.) Another example is setting the yard as the distance from the tip of England’s
King Henry I’s nose to the tip of his thumb. With the establishment of the National Bureau of Standards,
NIST’s predecessor, in 1901, the United States began the practice of standardizing all the units used in
the English System.
The second system is International system of Units, commonly called the metric system. The metric
system was originally developed in France in 1791. All metric units are calculated in multiples of ten,
unlike the English system which has numerous divisions depending on what unit is being used. The six
basic units in the metric system are the meter, kilogram, second, ampere, kelvin (for temperature), and the
candela (light). Since January 2, 1991, the metric system has been mandatory for all Federal agencies
(Federal Register, Vol. 56, No. 23, Page 160).
All numbers that are
BOLD are exact equivalents.
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