Federal Register Notice
(go to beginning of text)


Thursday
December 20, 1990


Department of Commerce


National Institute of Standards and Technology


Metric System of Measurement;
Interpretation of the International System
of Units for the United States


Interpretation of the
International System of Units
for the United States

This is a web version, including updated addresses, of the December 20, 1990 Federal Register notice.

This notice restates the interpretation of the SI for the United States by the Department of Commerce. As provided by U.S. law, the metric system of measurement to be used in the United States is the SI as established by the General Conference on Weights and Measures and interpreted or modified for the United States by the Secretary of Commerce. The Secretary has delegated this authority to the Director of the National Institute of Standards and Technology.

Citation:
Federal Register  /  Vol. 55, No. 245, pp. 52242-52245  /  Thursday, December 20, 1990  /  Notices

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DEPARTMENT OF COMMERCE
National Institute of Standards and Technology

[Docket No. 900663-0163]

Metric System of Measurement;
Interpretation of the International System of Units for the United States

Agency: National Institute of Standards and Technology, Commerce.

ACTION: Notice.


SUMMARY: This notice restates the interpretation of the Department of Commerce as to the International System of Units (``SI'') for the United States. This interpretation was last published by the Department of Commerce in the Federal Register on February 26, 1982 (47 FR 8399-8400). Although the contents of the tables have not been changed in any significant way since 1982, in view of the amendment of the Metric Conversion Act of 1975 by the Omnibus Trade and Competitiveness Act of 1988, and because over eight years have elapsed since the above Federal Register notice was published, it is deemed appropriate to once again issue tables and associated text setting forth the interpretation of the SI for the United States.

FOR FURTHER INFORMATION CONTACT: For information regarding the International System of Units, Dr. Barry N. Taylor, Building 225, Room B161, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-0001, telephone number (301) 975-4220. For more information regarding the Federal Government's program for use of the International System of Units, Mr. James B. McCracken, Metric Program Office, Building 820, Room 306, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-0001, telephone number (301) 975-3686.

SUPPLEMENTARY INFORMATION: Section 5164 of Public Law 100-418, the Omnibus Trade and Competitiveness Act of 1988, amends Public Law 94-168, the Metric Conversion Act of 1975. In particular, section 3 of the latter act is amended to read as follows:

``Sec. 3. It is therefore the declared policy of the United States -

``(1) to designate the metric system of measurement as the preferred system of weights and measures for United States trade and commerce:

``(2) to require that each Federal agency, by a date certain and to the extent economically feasible by the end of the fiscal year 1992, use the metric system of measurement in its procurements, grants, and other business related activities, except to the extent that such use is impractical or is likely to cause significant inefficiencies or loss of markets to United States firms, such as when foreign competitors are producing competing products in non-metric units;

``(3) to seek ways to increase understanding of the metric system of measurement through educational information and guidance and in Government publications; and

``(4) to permit the continued use of traditional systems of weights and measures in nonbusiness activities.''

Section 403 of Public Law 93-380, the Education Amendments of 1974, states that it is the policy of the United States to encourage educational agencies and institutions to prepare students to use the metric system of measurement as part of the regular education program. Under both this act and the Metric Conversion Act of 1975, the ``metric system of measurement'' is defined as the International System of Units as established in 1960 by the General Conference on Weights and Measures and interpreted or modified for the United States by the Secretary of Commerce (sec. 4(4), Pub. L. 94-168; sec. 403(a)(3), Pub. L. 93-380). The Secretary has delegated his authority under these subsections to the Director of the National Institute of Standards and Technology.

In implementation of this authority, tables and associated materials were published in the Federal Register of February 26, 1982 (47 FR 8399-8400), setting forth the interpretation and modification of the International System of Units (hereinafter ``SI'')for the United States.

Although the contents of the tables have not been changed in any significant way since 1982, in view of the amendment of the Metric Conversion Act of 1975 by the Omnibus Trade and Competitiveness Act of 1988, and because over eight years have elapsed since the above Federal Register notice was published, it is deemed appropriate to once again issue tables and associated text setting forth the interpretation of the SI for the United States.

The SI is constructed from seven base units for independent quantities plus two supplementary derived dimensionless units for the dimensionless derived quantities plane angle and solid angle, as listed in Tables 1a and 1b.

Units for all other quantities are derived from these nine units. For example, in Table 2 are listed a number of SI derived units obtained from the base units in a coherent manner, which means, in brief, that they are expressed as products and quotients of the seven base units without numerical factors.

Certain derived units that have been given special names and symbols are listed in Table 3. They may themselves be used to express other derived units, as is shown in Table 4. All the derived units given in Tables 3 and 4 have been obtained from the base and supplementary units in the same coherent manner indicated above.

The supplementary units of Table 1b may be used in the expression of derived units as for the lumen in Table 3. Some additional examples are given in Table 5.

Table 6 gives the 16 prefixes used to form multiples and submultiples of the SI units. It is important to note that the kilogram is the only SI unit with a prefix as part of its name and symbol. Because double prefixes may not be used, in the case of mass the prefixes of Table 6 are to be used with gram (symbol g) and not with kilogram (symbol kg).

Certain units are not part of the SI, but are important and widely used. The units in this category that are accepted for use in the United States with the International System are listed in Table 7.

In those fields where their usage is already well established, the use of the units in Table 8 for a limited time is accepted, subject to future review.

As stated in the 1982 notice, metric units, symbols, and terms that are not in accordance with the foregoing interpretation are no longer accepted for continued use in the United States with the International System of Units. Accordingly, the following units and terms listed in the table of metric units in section 2 of the Act of July 28, 1866 that legalized the metric system of weights and measures in the United States are no longer accepted for use is the United States:

myriameter
stere
millier or tonneau
quintal
myriagram
kilo (for kilogram).

Although there is no formal comment period, public comments are welcome on a continuing basis. Comments should be submitted to Dr. Barry N. Taylor at the above address.

John W. Lyons,
Director
[FR Doc. 90-21913 Filed 12-19-90; 8:45 am]


The following material is not part of the Federal Register notice.

Note 1: At the suggestion of its Consultative Committee for Units (CCU, Comité Consultatif des Unités), the International Committee for Weights and Measures (CIPM, Comité International des Poids et Mesures) adopted four new SI prefixes at its September 1990 meeting. These new prefixes were approved by the 19th General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures) at its September-October 1991 meeting. Thus the new prefixes, which are given in Note 1 Table, have become officially part of the SI and hence of Table 6.

Note 2: In 1980, the CIPM, which is under the authority of the CGPM, interpreted the radian and steradian as so-called dimensionless derived units for which the CGPM allows the freedom of using or not using them in expressions for SI derived units. In 1995, the CIPM, at the request of its CCU, asked the 20th CGPM to eliminate formally the class of supplementary units as a separate class in the SI. The 20th CGPM approved this request at its October 1995 meeting and thus the SI now consists of only two classes of units: base units and derived units, with the radian and steradian subsumed into the class of derived units of the SI. This means that Table 1b is now officially part of Table 3. The option of using the radian and steradian in expressions for other SI derived units or not using them, as is convenient, remains unchanged.