Metric PracticeGuide for theWelding Industry

AWS A1.1:2001An American National Standard

550 N.W. LeJeune Road, Miami, Florida 33126

AWS A1.1:2001An American National Standard

Approved byAmerican National Standards Institute

October 1, 2001

Metric Practice Guidefor the Welding Industry

Supersedes ANSI/AWS A1.1:1998

Prepared byAWS A1 Committee on Metric Practice

Under the Direction ofAWS Technical Activities Committee

Approved byAWS Board of Directors

AbstractThis metric practice guide is based on the International System of Units (SI) as defined in the U.S. Federal Register

notice of July 28, 1998, Metric System of Measurement: Interpretation of the International System of Units for theUnited States. It includes the base units, derived units, and rules for their use. Also covered are conversion factors andrules for their use in converting inch-pound units to SI units.

Recommendations are presented for style and usage in such areas as prefixes, punctuation, number grouping, etc.There are also suggestions to industry for managing the transition.

Key WordsMetric practice, SI units, conversions, round-off rules, preferred numbers

vii

Table of ContentsPage No.

Personnel .................................................................................................................................................................... iiiForeword .......................................................................................................................................................................vList of Tables............................................................................................................................................................. viii1. Scope ......................................................................................................................................................................12. The International System of Units (SI) ..................................................................................................................1

2.1 Completeness .................................................................................................................................................12.2 Coherence.......................................................................................................................................................12.3 Uniqueness .....................................................................................................................................................12.4 Advantages of the SI ......................................................................................................................................1

3. SI Units and Symbols .............................................................................................................................................13.1 SI Base Units..................................................................................................................................................23.2 SI Derived Units.............................................................................................................................................23.3 Prefixes...........................................................................................................................................................2

4. Other Units Used with SI .......................................................................................................................................25. Units Pertaining to Welding ...................................................................................................................................26. Style and Usage ......................................................................................................................................................2

6.1 Application and Usage of Prefixes.................................................................................................................26.2 Mass, Force, and Weight ................................................................................................................................56.3 Temperature....................................................................................................................................................56.4 Time ...............................................................................................................................................................66.5 Angles ............................................................................................................................................................66.6 Stress and Pressure.........................................................................................................................................66.7 Capitalization .................................................................................................................................................66.8 Plurals.............................................................................................................................................................66.9 Punctuation.....................................................................................................................................................76.10 Writing Numbers............................................................................................................................................76.11 Miscellaneous Styling ....................................................................................................................................7

7. Conversions ............................................................................................................................................................87.1 Rules for Converting and Rounding...............................................................................................................87.2 Inch to Millimeter Conversion .......................................................................................................................87.3 Other Conversions........................................................................................................................................127.4 Round-Off Rules ..........................................................................................................................................13

8. Transition..............................................................................................................................................................138.1 Introduction..................................................................................................................................................138.2 Considerations..............................................................................................................................................13

9. Preferred Numbers................................................................................................................................................149.1 Definition .....................................................................................................................................................149.2 Application of Preferred Numbers ...............................................................................................................159.3 Value of Using Preferred Numbers ..............................................................................................................15

AnnexesNonmandatory InformationAnnex AInch to Millimeter Conversion ...................................................................................................................17Annex BPounds-Force per Square Inch to Kilopascal Conversion .........................................................................19Annex CFahrenheitCelsius Temperature Conversion............................................................................................21Annex DOther Documents ......................................................................................................................................25Annex EOther Organizations ..................................................................................................................................27Annex FUnits for Newtons Second Law ................................................................................................................29Annex GGuidelines for Preparation of Technical Inquiries for AWS Technical Committees .................................31

viii

List of TablesTable Page No.

1 SI Base Units..................................................................................................................................................22 Examples of SI Derived Units........................................................................................................................33 SI Prefixes ......................................................................................................................................................44 Other Units Which May be Used with SI Units.............................................................................................45 Units Pertaining to Welding ...........................................................................................................................56 Filler Metal Sizes ...........................................................................................................................................67 Fillet Sizes......................................................................................................................................................68 General Conversions ......................................................................................................................................99 Conversions for Common Welding Terms ...................................................................................................10

10 Millimeter Value Round-Off Using Inch Tolerance Span............................................................................1111 Comparison of Round-Off Methods A and B ..............................................................................................1112 Basic Preferred NumbersDecimal Series .................................................................................................16

AWS A1.1:2001

1

1. ScopeThis metric practice guide is based on the Inter-

national System of Units (SI) as defined in the U.S. Fed-eral Register notice of July 28, 1998, Metric System ofMeasurement: Interpretation of the International Systemof Units for the United States. (Other source documentsand style guides are referenced in Annex D.) This guidecontains specifications of the SI base units, derived units,prefixes, and rules for their use in AWS documents andby the welding industry. It also contains factors and rulesfor converting from inch-pound units (often referred to asU.S. Customary Units) to SI Units and recommendationsto industry for managing the transition.

2. The International System of Units (SI)A system of units is any collection of related units.

SI is the only system that has the properties outlined in2.12.3.

2.1 Completeness. Completeness requires that a unit ofmeasurement be defined for every quantity of interest inthe physical sciences and technologies.

2.2 Coherence. Coherence requires that all derived unitsin the system be obtained from the base units by the rulesof multiplication and division with no numerical factorother than the number one (1) ever occurring in the ex-pressions for derived units in terms of the base units. Thesystem of units must also be coherent with its corre-sponding system of quantities and equations. A systemof units is coherent with respect to a system of quantitiesand equations if the system of units is chosen in such away that the equations between numerical values haveexactly the same form (including numerical factors) asthe corresponding equations between quantities.

2.3 Uniqueness. Uniqueness requires that there be one,and only one, unit defined for each quantity. For exam-ple, the SI Units for force (newton), energy (joule), andpower (watt) are the same, respectively, whether the pro-cess is mechanical, electrical, or thermal.

2.4 Advantages of the SI. The International System ofUnits (SI) is the metric system of units in its latest form.SI is the only system of units which fully satisfies all theabove three requirements for completeness, coherence,and uniqueness. Within SI, a set of base-ten prefixes isdefined to form decimal multiples and submultiples of SIUnits. SI Units and their base-ten multiples and submul-tiples are in harmony with our decimal system of arith-metic, facilitating easy numerical calculations. Awkwardmanipulations of common fractions such as 1/16, 1/32,and 1/64 are completely unnecessary. All industrial na-tions, including the United States by the Omnibus Tradeand Competitiveness Act of 1988 (Public Law 100-418),have chosen the SI as the preferred system of units for allapplications in science, engineering, technology, com-merce, and trade.

3. SI Units and SymbolsSI consists of seven base units, derived units, and a set of

prefixes for the formation of multiples of the various units.

Metric Practice Guidefor the Welding Industry

QuantityDerived

Unit Unit Equation

Force (mass times acceleration)F = m a

newton 1 N = 1 kg m/s2

Energy (force times distance)E = F l

joule 1 J = 1 N m

Power (rate of energy transfer)P = E/t

watt 1 W = 1 J/s

Pressure (force divided by area)p = F/A

pascal 1 Pa = 1 N/m2