Metric Usage

Section Renumbered 8/06

  1. Metrication Policy
  2. Definitions
  3. Scope of Metrication
  4. Responsibilities
  5. Implementation Guidelines
    1. SI Units: Definitions
    2. Metric Practice
    3. New Design and Development
    4. Repair, Modification, and Retrofit of Existing Inch-Pound Facilities and Equipment
    5. Tools and Equipment
    6. Technical Documentation
    7. Deviation from SI Usage
    8. Reference


The Laboratory requires the use of the modern metric system, the International System of Units (abbreviated SI, from the French Système International d'Unités), except when safety considerations dictate otherwise or when metric usage would entail excessive costs or otherwise seriously impede Laboratory operations. Exceptions are also allowed for programs whose sponsors specify the use of the inch-pound system. Division directors are responsible for implementing the metric system within their respective divisions as expediently as feasible.

The Laboratory has adopted SI units in response to Trade and Competitiveness Act of 1988 §5164, Executive Order 12770 of 1991, and DOE Order 5900.2.


Metric System. In general parlance, any of a number of closely related decimal unit systems, including the centimeter-gram-second (cgs) system, the meter-kilogram-second (MKS) system, the meter-kilogram-second-ampere (MKSA) system, and the current International System of Units (SI). As used in this section, the expressions metric, metric system, and metric units refer exclusively to the International System of Units.

International System of Units (SI). The modern metric system (i.e., the system of decimal units currently defined and sanctioned by the International Bureau of Weights and Measures, which operates under the authority of the General Conference on Weights and Measures).

Metrication. The process of expanding the use of SI units and phasing out the use of non-SI units.

Inch-Pound System. The system of measurement units most commonly used in the United States. This system is based on such units as the inch, pound, second, and degree Fahrenheit. It is also frequently referred to as the "English System" or the "U.S. System."

Hard Metric Usage (or Practice). Exclusive and direct use of SI units (i.e., without first converting measurements made using inch-pound or other non-SI units into SI equivalents). Hard metric usage generally means that a product will differ physically from an analogous product designed and produced using the inch-pound system. For example, a mechanical designer working in the inch-pound system might specify the thickness of a flat metal part as 1 inch. Working in "hard metric," the same designer might specify the thickness of this part as 25 mm.

Soft Metric Usage (or Practice). The conversion of inch-pound or other non-SI measurements to equivalent SI units, within the established measurement tolerances. In general, "soft metric" products will not differ physically from analogous products fabricated using the inch-pound system. Working in "soft metric," the mechanical designer in the example above would specify that the flat metal part in question must be exactly 25.4 mm thick.

Metric Design. Design work that incorporates SI usage. For purposes of this document, metric design generally means hard metric design, although soft metric design will be acceptable during the transition from inch-pound to SI units.

Dual Dimensioning. The inclusion of both SI and non-SI dimensions in drawings and publications.

Dual Indication. The inclusion of both SI and non-SI units and calibrations on instruments and gauges.

Hybrid Practice. Mixing SI units and non-SI units in an activity or a product.


The Laboratory aims to implement the use of SI units throughout its operations as rapidly as it is reasonable and cost-effective to do so. In principle, all research programs, facilities, and equipment are subject to metrication. The Laboratory's divisions are granted latitude, however, to determine the pace and stages of metric conversion. In general, postponement of metrication should be allowed only in situations in which metric conversion would seriously impede Laboratory operations.


All Laboratory planning, design, procurement, manufacturing, installation, integration, testing, operation, and maintenance must be performed in a manner consistent with the provisions of this policy. Division directors will be responsible for ensuring adherence to these guidelines within their respective divisions.


1.  SI Units: Definitions

SI as currently defined is based on seven units that are considered dimensionally independent: the meter, kilogram, second, ampere, kelvin, mole, and candela. All other units are derived from these base units and two supplemental units that are considered dimensionless derived units: the radian and the steradian. Information on the base, supplemental, and derived units are given in ASTM E 380-92, Standard Practice for Use of the International System of Units (SI) (the Modernized Metric System) (ASTM, Philadelphia, 1992).

2.  Metric Practice

Metric practice at the Laboratory will conform to the provisions of ASTM E 380-92 and subsequent revisions of that document. ASTM E 380-92 prescribes standards of usage governing the following issues:

ASTM E 380-92 also provides comprehensive tables of conversion factors.

Contrary to the style used in ASTM E 380-92, Laboratory drawings and publications will use the spellings "meter" and "liter" instead of "metre" and "litre." The Laboratory also expressly sanctions the use of the degree Celsius in place of the Kelvin in all contexts except formal scientific publications.

If multiple codes and standards exist governing specific disciplines and trades (e.g., fasteners), the Laboratory Metric Transition Council will be responsible for adopting the code or standard most appropriate for the Laboratory. The Metric Transition Council is chaired by the Engineering Division Director.

3.  New Design and Development

Metric design is preferred in all new projects. Major projects nearing completion that have been designed and constructed in the inch-pound system may be completed in that system. Materials, components, parts, subassemblies, and semifabricated materials of commercial design will be specified in SI units except when exemptions are granted on the basis of the criteria listed in Paragraph (E)(7), below. Bulk materials will be specified and accepted in SI units for projects and items designed and specified using SI units.

4.  Repair, Modification, and Retrofit of Existing Inch-Pound Facilities and Equipment

Repair, modification, and retrofit of existing facilities and equipment of inch-pound design using SI-designed items are permissible. Decisions concerning such modification will be determined on a case-by-case basis, however, with consideration given to the technical and economic feasibility of using SI and to other relevant factors such as safety. The final decision in such cases will be made by the project leader with the concurrence of the responsible division director. In general, increasing use of SI-designed items is strongly encouraged.

5.  Tools and Equipment

For the foreseeable future, shop, laboratory, and general-purpose tools and test equipment used by Laboratory personnel must permit work in either SI or inch-pound units or in both, depending on which system is encountered in work situations. The purchase and assignment of tools and equipment must take this requirement into account, though gradual conversion to pure metric usage is expected to reduce its importance over time.

6.  Technical Documentation

Technical documentation and Laboratory publications will comply with the following requirements:

  1. Specifications and Engineering Drawings for New Designs and Modifications of Existing Designs. These engineering documents must incorporate SI units in either of two ways. The preferred method is SI units only. Alternatively, dual dimensioning may be used. If dual dimensioning is used, the general rule will be for SI units to be given first, with the corresponding non-SI units following in parentheses. In cases in which safety is a prime consideration and with the approval of the responsible division director, engineering documents may use dual dimensioning with inch-pound units first and SI units following in parentheses.

  2. Engineering Calculations. All engineering calculations that contribute to metric designs must be expressed in SI units.

  3. Laboratory Publications. Metric units must be used in all Laboratory reports and publications. Exclusive use of SI units is preferred wherever possible, but dual dimensioning is allowed during the transitional period. If dual dimensions are used, the preferred format is SI units first and the corresponding inch-pound units in parentheses. For cases in which safety is a prime concern, publications may provide dual dimensions with inch-pound units first and SI units following in parentheses.

7.  Deviation from SI Usage

Deviation from SI usage may be approved by the responsible division director. Acceptable criteria for allowing continued use of non-SI units include such factors as:

8.  Reference

For more information, see Guidelines for Metrication at Lawrence Berkeley Laboratory (LBNL/PUB-729), which is available from the Metric Transition Council.

Printed . The official or current version is located in the online LBNL Requirements and Policies Manual.
Printed or electronically transmitted copies are not official. Users are responsible for working with the latest approved revision.

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