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JANUARY 27, 1993


MAY 5, 1983




This standard was developed by the Standards and Metric Practices Subcommittee of the Metrication Operating Committee, which operates under the Interagency Council on Metric Policy. It is the basic Federal standard that lists metric units recommended for use throughout the Federal government, and is specified in the Federal Standardization Handbook, issued by the General Services Administration in accordance with 41 CFR 101-29. Before issue, it was coordinated with the departments and agencies of the Interagency Council on Metric Policy.

The General Services Administration has authorized the use of this Federal standard by all Federal agencies.

Civilian Agency Coordinating Activity:

Federal Supply Service, General Service Administration

Military Agency Coordinating Activity:

Standardization Program,
Office of the Assistant Secretary (Production and Logistics),
Department of Defense

Preparing Activity:

Metric Program,
National Institute of Standards and Technology,
Technology Administration,
Department of Commerce


When a federal agency determines that there is a need for a revision of this standard, a written request for revision should be submitted to the General Services Administration, Federal Supply and Service, Environmental and Engineering Policy Division (FCRE), Washington, DC 20406. The request shall include data that support the proposed change. The Metric Program, National Institute of Standards and Technology, as custodian of this standard, will coordinate all proposed changes with the Metrication Operating Committee.

Table of Contents

1. Scope
2. Authoritative Document
3. Definitions
4. General Requirements
5. Detailed Requirements
Alphabetical Index


This standard lists preferred metric units (See 4.1) recommended for use throughout the Federal Government. It gives guidance on the selection of metric units required to comply with the provisions of the Metric Conversion Act of 1975 (P.L. 94-168), as amended by the Omnibus Trade and Competitiveness Act of 1988 (P.L. 100-418), and Executive Order (EO) 12770 of July 25, 1991. The guidance in this standard applies to, but is not limited to, the drafting of laws, regulations, contracts, and purchase orders; and the preparation of reports, statistical tables, and databases.


The following document forms the authoritative basis of this standard to the extent specified herein:

American National Standard for Metric Practice, ANSI/IEEE Std 268-1992, Institute of Electrical and Electronics Engineers, Inc.


3.1 SI Units. Units belonging to the International System of Units, which is abbreviated SI (from the French Le Système International d'Unités), as interpreted or modified for use in the United States by the Secretary of Commerce (55 F.R. 52242, Dec. 20, 1990).

3.2 Inch-pound Units. Units based upon the yard and the pound, commonly used in the United States, and defined by the National Bureau of Standards (now the National Institute of Standards and Technology). In this standard, the term inch-pound unit includes other customary units, such as the degree Fahrenheit, used extensively in the United States at present. Some inch-pound units used in the United States, such as the gallon, have the same name as units previously used in other countries but differ in magnitude.


4.1 Preferred Metric Units. Preferred metric units for use throughout the Federal Government are:

The preferred metric units listed in Section 5 of this standard have been selected in accordance with the recommendations of ANSI/IEEE Std 268.

4.1.1 SI Base Units and Supplementary Units. The SI is constructed from seven base units for independent quantities¹ plus the two supplementary units for plane angle and solid angle.

Quantity Unit Name Unit Symbol
length meter m
mass² kilogram kg
time second S
electric current ampere A
thermodynamic temperature kelvin K
amount of substance mole mol
luminous intensity candela cd
plane angle radian rad
solid angle steradian sr

4.1.2 SI Derived Units. Derived units are formed by combining base units, supplementary units, and other derived units according to the algebraic relations linking the corresponding quantities. The symbols for derived units are obtained by means of the mathematical signs for multiplication, division, and use of exponents. For example, the SI unit for velocity is the meter per second (m/s or m·s-1), and that for angular velocity is the radian per second (rad/s or rad·s-1). Some derived SI units have been given special names and symbols, as follows:

Quantity Unit Name Unit Symbol Expression in
Terms of Other
SI Units
Absorbed dose, specific
energy imparted,
kerma, absorbed dose index
gray Gy J/kg
Activity (of a radionuclide) becquerel Bq 1/s
Celsius temperature degree Celsius °C K
Dose equivalent sievert Sv J/kg
Electric capacitance farad F C/V
Electric charge,
quantity of electricity
coulomb C A·s
Electric conductance siemens S A/V
Electric inductance henry H Wb/A
Electric potential,
potential difference,
electromotive force
volt V W/A
Electric resistance ohm Ω V/A
Energy, work, quantity of heat joule J N·m
Force newton N kg·m/s²
Frequency (of a
periodic phenomenon)
hertz Hz 1/s
Illuminance lux lx lm/m²
Luminous flux lumen lm cd·sr
Magnetic flux weber Wb V·s
Magnetic flux density tesla T Wb/m²
Power, radiant flux watt W J/s
Pressure, stress pascal Pa N/m²

4.1.3 SI Prefixes. The common metric prefixes are:

Multiplication Factor Prefix Name Prefix Symbol
1 000 000 000 000 = 10¹² tera T
1 000 000 000 = 10⁹ giga G
1 000 000 = 10⁶ mega M
1 000 = 10³ kilo k
100 = 10² hecto h
10 = 10¹ deka da
0.1 = 10⁻¹ deci d
0.01 = 10⁻² centi c
0.001 = 10⁻³ milli m
0.000 001 = 10⁻⁶ micro mu
0.000 000 001 = 10⁻⁹ nano n
0.000 000 000 001 = 10⁻¹² pico p

These prefixes are part of SI. They are attached to an SI unit name or symbol to form what are properly called “multiples” and “submultiples” of the SI unit. Prefixes produce units that are of an appropriate size for the application, e.g., millimeter or kilometer. Examples that show reasonable choices of multiples and submultiples for many practical applications are given in Section 5. While all combinations are technically correct, many are not used in practice. The prefixes deci, deka, and hecto are rarely used; prefixes that are multiples or submultiples of 1000 are generally preferred. When the unit name is written in full, the prefix is written in full: megahertz, not Mhertz. When the unit symbol is used, the symbol is used: MHz, not megaHz. Only one prefix should be used in forming a multiple of an SI unit, e.g., Mg, not kkg; or pV, not mmV. Prefix symbols for the values a million or greater are capitalized and those below a million are written in lower case.

4.1.4 Editorial Style. The names of all SI units begin with a lower case letter except, of course, at the beginning of a sentence or when other grammar rules dictate capitalizing nouns. There is one exception: in “degree Celsius” the term “degree” is lower case but “Celsius” is always capitalized. Unit symbols are always written in lower case except for the liter and those units derived from the name of a person (e.g., W for watt, Pa for pascal, etc.). SI symbols are unique “letter shorthand” for unit names – they are not abbreviations and should therefore not be followed by a period (except at the end of a sentence). Likewise, symbols stand for both the singular and plural of the unit and should not have an s added. SI units are always written in an upright typeface with a space between the numeric value and the symbol. See ANSI/IEEE Std 268 and other documents listed in the Bibliography for further usage rules.

4.2 Accepted Units. For practical reasons a number of non-metric units are accepted for use. These include units of time (minute, hour, etc.), units of plane angle (degree, etc.), and a few units for special applications, such as the nautical mile, used in navigation. Section 5 includes accepted units and shows their areas of application. These units may be used in full compliance with the provisions of the amended Metric Conversion Act, EO 12770, and the Federal Register Notice, “Metric System of Measurement; Interpretation of the International System of Units for the United States” (55 F.R. 52242, Dec. 20, 1990).

4.3 Unacceptable Metric Units. Many older metric practices do not comply with the amended Metric Conversion Act, EO 12770, and 55 F.R. 52242. Particular care shall be taken to avoid introducing non-SI practices into the United States in areas where such practices are not now established. The units listed in the following three subsections shall not be used.

4.3.1 CGS Units. Units with special names peculiar to the various cgs (centimeter-gram-second) systems shall not be used. Among these units are the following that have been commonly used:

erg, dyne, gal used in mechanics
poise, stokes used in fluid dynamics
stilb, phot, lambert used in photometry
emu, esu, gauss, oersted, maxwell, gilbert, biot,
franklin, abampere, abvolt, statvolt, etc.
used in electricity and magnetism

4.3.2 Deprecated Names or Symbols. Other units from older versions of the metric system and metric jargon that shall not be used include:

Incorrect term Correct Unit
kilo kilogram
are square dekameter
candle or
fermi femtometer
gamma nanotesla
micron micrometer
millimicron nanometer
mho siemens
rho microgram
lambda cubic millimeter or microliter

4.3.3 Miscellaneous Non-SI Units Not to be Used. Additional units that are not accepted for use include the following:

g as a unit of acceleration (g = 9.81 m/s²)
grade or gon [1 grade = (pi/200) rad]
langley (1 langley = 1 cal/cm²)
metric carat
metric horsepower
millimeter of mercury
millimeter, centimeter, or meter of water
standard atmosphere (101.325 kPa)
technical atmosphere (98.0665 kPa)
torr (133.322 Pa)

4.4 Conversion. Conversion factors in Section 5 are shown from inch-pound units to metric units, generally to seven significant digits. The first column, labeled From, lists inch-pound and other units commonly used to express the quantities; the second column, labeled To, gives SI units or other preferred units; and the third column, labeled Multiply By, gives the conversion factors by which the numerical value in From units must be multiplied to obtain the numerical value in To units. For conversion from inch-pound units to metric units, multiply by the factor. For example, to convert 10.1 feet to meters multiple by 0.3048; the answer is 3.078 meters, which can be rounded to 3.08 meters (see Section 4.5 on rounding). For conversion from metric units to inch-pound units, divide rather than multiply by the factor. For example, to convert 16.3 meters to yards divide by 0.9144; the answer is 17.826 yards, which can be rounded to 17.8 yards.

4.5 Rounding. For rounding of metric values obtained by conversion from inch-pound values, the following simplified rules are suggested. A more complete treatment of rounding rules is given in Appendix C of ANSI/IEEE Std 268.

4.5.1 If the inch-pound value is expressed by a combination of units such as feet and inches, or pounds and ounces, it should first be converted to the smaller unit.


4.5.2 Multiply the inch-pound value by the conversion factor. If the first significant3 digit of the metric value is equal to or greater than the first significant digit of the inch-pound value, round the metric value to the same number of significant digits as there are in the inch-pound value.


If the first significant digit of the metric value is smaller than the first significant digit of the inch-pound value, round to one more significant digit.


4.5.3 When the digits to be discarded begin with a 5 or more, increase the last digit retained by one.


4.5.4 It is essential to use good judgment in estimating the precision required in conversions.


Do not retain more digits than is appropriate for the situation.

4.5.5 Where an inch-pound value represents a maximum or minimum limit that must be respected, the rounding must be in the direction that does not violate the original limit.

4.5.6 Normally, temperatures expressed in a whole number of degrees Fahrenheit should be converted to the nearest 0.5 K (or degree Celsius). As with other quantities, the number of significant digits to retain will depend upon the implied accuracy of the original temperature.


This section gives detailed requirements for the selection of units, consistent with ANSI/IEEE Std 268. The subsections list conversion factors to the appropriately sized metric unit, either an SI unit with appropriate prefix or a non-SI unit that is accepted for use with SI. ANSI/IEEE Std 268, which has been recommended by the Metrication Operating Committee of the Interagency Council on Metric Policy for use by all agencies and departments of the Federal Government, lists conversion factors to SI units only. The SI units are the coherent set of base, supplementary, and derived units without prefixes, except for the base unit kilogram.

Government agencies may develop supplemental lists of accepted units applicable to their special fields. Such supplemental lists shall be consistent with this Federal Standard and with ANSI/IEEE Std 268.

Other Derived Quantities. It is not practical to list all quantities, but others not listed can be readily derived using the conversion factors given. For example, to convert from inches per second to centimeters per second, multiply by 2.54; to convert from Btu per pound to joules per kilogram, multiply by (1055.056)/(0.453 592 37) or 2326.

Note on Mixed Units and Fractions. Mixed units, which are commonly used with inch-pound units, are not used in metric practice. Thus, while a distance may be given in inch-pound units as 27 ft, 5 in, metric practice shows a length as 3.45 m rather than 3 m, 45 cm. Binary fractions (such as 1/2 or 3/8) are not used with metric units. For example, a person's weight is given as 70.5 kg, not 70-1/2 kg.

Preferred units for various quantities are grouped in the following subsections by: Space and Time, Mechanics, Heat, Electricity and Magnetism, Light, and Radiology. (These groupings are consistent with the groupings in ANSI/IEEE Std 268.) The quantities under each group are listed in italic type. The first column, labeled From, lists inch-pound and other units commonly used to express the quantities; the second column, labeled To, gives SI units or other preferred units; and the third column, labeled Multiply By, gives the conversion factors (generally to seven significant digits) by which the numerical value in From units must be multiplied to obtain the numerical value in To units. 51 units and their submultiples or multiples, in the To column, are in bold type. The liter, hectare, and metric ton and other accepted units (see 4.2), in the To column, are in normal type. Conversion factors, in the Multiply By column, that are exact are in bold type.

5.1 Quantities of Space and Time

5.1.1 Plane angle

NOTE: No change in U.S. customary usage is required for plane angle units. The radian, which is the SI unit, is most frequently used in scientific or technical work and in forming derived units. Use of the degree and its decimal fractions is permissible. Use of the minute and second is discouraged except for specialized fields such as cartography.

5.1.2 Solid angle

NOTE: No change in U.S. customary usage is required for solid angle units. The steradian, which is the only unit commonly used to express solid angle, is an SI unit.

5.1.3 Length

ångström nanometer (nm) 0.1
fathom meter (m) 1.828 8
foot meter (m) 0.304 8
foot [U.S. survey] meter (m) 0.304 800 6

NOTE: In 1893 the U.S. foot was legally defined as 1200/3937 meters. In 1959 a refinement was made to bring the foot into agreement with the definition used in other countries, i.e. 0.3048 meters. At the same time it was decided that any data in feet derived from and published as a result of geodetic surveys within the U.S. would remain with the old standard, which is named the U.S. survey foot. The new length is shorter by exactly two parts in a million. The five-digit multipliers given in this standard for acre and acre-foot are correct for either the U.S. survey foot or the foot of 0.3048 meters exactly. Other lengths, areas, and volumes are based on the foot of 0.3048 meters.

inch centimeter (cm) 2.54
millimeter (mm) 25.4
microinch micrometer (mu m) 0.025 4
mil millimeter (mm) 0.025 4
micrometer (mu m) 25.4
yard meter (m) 0.9144
mile kilometer (km) 1.609 344
nautical mile kilometer (km) 1.852

NOTE: The nautical mile is an accepted unit for use in navigation.

point millimeter (mm) 0.351 46
pica millimeter (mm) 4.2175

5.1.4 Area

acre square meter(m²) 4 046.9
hectare (ha) 0.404 69

NOTE: The hectare, equal to 10 000m², is accepted for use with SI.

circular mil square millimeter(mm²) 0.000506 708
square inch square centimeter(cm²) 6.451 6
square millimeter(mm2) 645.16
square foot square meter(m²) 0.092 903 04
square yard square meter(m²) 0.836 127 4
square mile square kilometer(km²) 2.589988

5.1.5 Volume

acre-foot cubic meter (m3) 1 233.5
barrel, oil cubic meter (m3) 0.1589873
(42 U.S. gallons) liter (L) 158.9873

NOTES: (1) the liter, equal to 0.001 m3, is accepted for use with SI. (2) A variety of barrel sizes have been used for other commodities.

cubic yard cubic meter(m3) 0.764 555
cubic foot cubic meter(m3) 0.028 316 85
liter (L) 28.316 85
board foot cubic meter(m3) 0.002 359 737
register ton cubic meter(m3) 2.831 685

NOTE: The register ton is a unit of volume used to express the capacity of a ship. For example, a 20000-ton freighter has a capacity of approximately 57000 m3, measured in accordance with established procedures.

bushel cubic meter(m3) 0.035 23907

NOTE: Agricultural products that are sold by the bushel in the United States are often sold by weight in other countries. There can be a considerable variation in the weight per unit volume due to differences in variety, size, or condition of the commodity, tightness of pack, degree to which the container is heaped, etc. The following conversion factors are used by the U.S. Department of Agriculture for statistical purposes:

crop Weight per bushel(kg)
barley 21.5
corn, shelled 25.4
oats 14.5
potatoes, soybeans, wheat 27.2
gallon liter (L) 3.785 412
quart (liquid) liter (L) 0.946 352 9
pint (liquid) liter (L) 0.473 176 5
fluid ounce milliliter (mL) 29.573 53

NOTE: In the United States, the cup, tablespoon, and teaspoon are defined as 8, 1/2, and 1/6 fluid ounces, respectively. For practical usage the metric equivalents are 250 mL, 15 mL, and 5 mL.

cubic inch cubic centimeter (cm3) 16.387 06

5.1.6 Time

NOTE: No change in customary U.S. usage is required for time units. The second is the SI unit of time, but the minute and hour, as well as the day, week, year, etc., are accepted units.

5.1.7 Velocity

foot per second meter per second (m/s) 0.304 8
mile per hour kilometer per hour (km/h) 1.609 3
knot kilometer per hour (km/h) 1.852

NOTE: The knot, or nautical mile per hour, is an accepted unit for use in navigation.

5.1.8 Acceleration

inch per second squared meter per second squared (m/s²) 0.025 4
foot per second squared meter per second squared (m/s²) 0.304 8
standard acceleration of
gravity (g)
meter per second squared (ms²) 9.806 65

5.1.9 Flow rate

cubic foot per second cubic meter per second(m3/s) 0.028316 85
cubic foot per minute cubic meter per second(m3/s) 0.000471 947
liter per second (L/s) 0.471 9474
cubic yard per minute liter per second (L/s) 12.742 58
gallon per minute liter per second (L/s) 0.063 0902
gallon per day liter per day (L/d) 3.785 412

5.1.10 Fuel efficiency

mile per gallon kilometer per liter (km/L) 0.425 143 7

NOTE: To convert fuel efficiency in miles per gallon to fuel consumption in liters per 100 kilometers, use the formula:

235.2/(number of miles per gallon) = number of liters per 100 kilometers

5.2 Quantities of Mechanics

5.2.1 Mass (weight)

NOTE: There is ambiguity in the use of the term “weight” to mean either force or mass. In general usage, the term weight nearly always means mass and this is the meaning given the term in U.S. laws and regulations. Where the term is so used, weight is expressed in kilograms in SI. In many fields of science and technology the term “weight” is defined as the force of gravity acting on an object, i.e., as the product of the mass of the object and the local acceleration of gravity. Where weight is so defined, it is expressed in newtons in SI.

ton (long) kilogram (kg) 1 016.047
metric ton (t) 1.016 047

NOTE: The metric ton (referred to as “tonne” in many countries), equal to 1000 kg, is accepted for use with SI.

ton (short) kilogram (kg) 907.184 74
metric ton(t) 0.907184 7
slug kilogram (kg) 14.593 90
pound kilogram (kg) 0.453 592 37
ounce, troy gram (g) 31.10348
ounce, avoirdupois gram (g) 28.34952
grain milligram (mg) 64.79891

5.2.2 Moment of mass

pound foot kilogram meter (kg.m) 0.138255 0

5.2.3 Density

ton (short) per cubic yard kilogram per cubic meter
1 186.553
metric ton per cubic meter (t/m3) 1.186 553
pound per cubic foot kilogram per cubic meter (kg/m3) 16.01846

5.2.4 Concentration (mass)

pound per gallon gram per liter (g/L) 119.826 4
ounce per gallon gram per liter (g/L) 7.489152

5.2.5 Momentum

pound foot per second kilogram meter per second 0.138255 0

5.2.6 Moment of inertia

pound square foot kilogram square meter(kg.m²) 0.042 14011

5.2.7 Force

pound-force newton (N) 4.448222
poundal newton (N) 0.138255 0

5.2.8 Moment of force, torque

pound-force foot newton meter (N·m) 1.355 818
pound-force inch newton meter (N·m) 0.112 9848

5.2.9 Pressure, stress

standard atmosphere kilopascal (kPa) 101.325

NOTE: The SI unit for pressure and stress is the pascal, which is equal to the newton per square meter. This unit, its multiples, and submultiples are preferred for all applications.

bar kilopascal (kPa) 100

NOTE: The bar and its submultiples are accepted for limited use in meteorology only. lt is not accepted for use in the U.S. for other applications, e.g., as the unit of fluid pressure in pipes and containers. The appropriate SI multiples, e.g., kilopascal or megapascal, should be used instead.

millibar kilopascal (kPa) 0.1
per square inch
kilopascal (kPa) 6.894 757
per square inch
megapascal (MPa) 6.894 757
per square foot
kilopascal (kPa) 0.047 880 26
inch of mercury kilopascal (kPa) 3.386 38
foot of water kilopascal (kPa) 2.98898
inch of water kilopascal (kPa) 0.24884
millimeter of mercury kilopascal (kPa) 0.133 322 4

NOTE: The actual pressure corresponding to the height of a vertical column of fluid depends upon the local acceleration of gravity and the density of the fluid, which in turn depends upon the temperature. The conversion factors given here are conventional values adopted by the International Organization for Standardization (ISO).

torr pascal (Pa) 133.322 4

5.2.10 Viscosity (dynamic)

centipoise millipascal second (mPa·s) 1

5.2.11 Viscosity (kiniatic)

centistokes square millimeter
per second(mm²/s)

5.2.12 Energy, work, heat

kilowatthour megajoule (MJ) 3.6

NOTE: The kilowatthour is accepted as a unit of electrical energy only. The SI unit of energy, the joule, which is equal to the newton meter or the watt second, is recommended for all applications.

(as used in physics)
joule(J) 4.184

NOTE: The calorie listed here is the thermochemical calorie. Other values of the calorie have been used.

(as used in nutrition)
kilojoule (kJ) 4.184

NOTE: The calories used in nutrition is the same as the thermochemical kilocalorie. All use of the calorie is deprecated.

Btu kilojoule (kJ) 1.055 056

NOTE: The British Thermal Unit (Btu) used in this standard is the International Table Btu adopted by the Fifth International Conference on Properties of Steam, London, 1956.

therm (U.S.) megajoule (MJ) 105.480 4
horsepower hour megajoule (MJ) 2.684 520
foot pound-force
per second
joule (J) 1.355 818

5.2.13 Power

NOTE: Power is the rate of energy transfer. The SI unit for all forms of power, mechanical, electrical, and heat flow rates is the watt.

ton, refrigeration kilowatt (kW) 3.516 85
Btu per second kilowatt (kW) 1.055 056
Btu per hour watt (W) 0.293 071 1
(550 foot pounds-force
per second)
watt (W) 745.6999
horsepower, electric watt (W) 746
foot pound-force
per second
watt (W) 1.355818

5.3 Quantities of Heat

5.3.1 Temperature

NOTE: The SI unit for customary temperature is the degree Celsius (0C). In inch-pound units customary temperature is expressed in degrees Fahrenheit. The formula for converting customary temperature is: tc=(tf-32)/1.8

The SI unit for thermodynamic temperature TK is the kelvin (K). Celsius temperature is defined by the equation: tcc=TK-273.15 K. K,

The inch-pound unit for thermodynamic temperature is the degree Rankine. The formula for converting thermodynamic temperature is: TK = TR /1.8.

A temperature interval may be expressed in SI either in kelvins or in degrees Celsius, as convenient. The formula for converting a temperature interval At in degrees Fahrenheit into SI is: delta tK = delta tC= delta tF/1.8

5.3.2 Linear expansion coefficient

reciprocal degree reciprocal kelvin(K-1) or 1.8
Fahrenheit reciprocal degree Celsius(°C-1)

5.3.3 Heat

NOTE: Heat is a form of energy. See 5.2.12

5.3.4 Heat flow rate

NOTE: Heat flow rate is a form of power. See 5.2.13

5.3.5 Thermal conductivity

Btu inch per hour square watt per meter kelvin 0.144 227 9
foot degree Fahrenheit [W/(m°K)]

5.3.6 Coefficient of heat transfer

Btu per hour square foot watt per square meter 5.678263
degree Fahrenheit kelvin [W/(m²° K)]

5.3.7Heat capacity

Btu per degree Fahrenheit kilojoule per kelvin (kJ/K) 1.899 108

5.3.8Specific heat capacity

Btu per pound kilojoule per kilogram 4.186 8
degree Fahrenheit kelvin [kJ/(kg·K)]

NOTE: The quantities 5.3.5 through 5.3.8 are defined in terms of temperature interval. Therefore K may be replaced by °C.

5.3.9 Entropy

Btu per degree Rankine kilojoule per kelvin(kj/K) 1.899 108

5.3.10 Specific entropy

Btu per pound degree kilojoule per kilogram 4.186 8
Rankine kelvin [kJ/(kg·K)]

5.3.11 Specific internal energy

Btu per pound kilojoule per kilogram(kJ/kg) 2.326

5.4 Quantities of Electricity and Magnetism

NOTE: The common electrical units ampere (A), volt (V), ohm (Ω), siemens (S), coulomb (C), farad (F), henry (H), weber (Wb), and tesla (T) are SI units that are already in use in the United States. The various cgs units shall no longer be used.

5.4.1 Magnetic field strength

oersted ampere per meter (A/m) 79.57747

5.4.2 Magnetic flux

maxwell nanoweber (nWb) 10

5.4.3 Magnetic flux density

gauss millitesla (mT) 0.1

5.4.4 Electric charge

ampere hour coulomb (C) 3 600

5.4.5 Resistivity

ohm circular mil
per foot
nanoohm meter (nΩ·m) 1.662 426

5.4.6 Conductivity

mho per centimeter siemens per meter (S/m) 100

5.5 Quantities of Light and Related Electromagnetic Radiation

NOTE: No change in U.S. customary usage is required for the following quantities: radiant intensity, watt per steradian (W/sr); radiance, watt per steradian square meter (W/(sr·m²); irradiance, watt per square meter (W/m²); luminous intensity, candela (cd); luminous flux, lumen (lm); and quantity of light, lumen second(lm· s).

5.5.1 Wavelength

ångström nanometer (nm) 0.1

5.5.2 Luminance

lambert candela per square
meter (cd/m²)
3 183.099
candela per square inch candela per square
meter (cd/m²)
1 550.003
footlambert candela per square
meter (cd/m²)
3.426 259

5.5.3 Luminous exitance

lumen per square foot lumen per square
meter (lm/m²)
10.763 91

5.5.4 llluminance

footcandle lux (lx) 10.763 91

5.6 Quantities of Radiology

5.6.1 Activity (of a radionuclide)

curie megabecquerel (MBq) 37000

5.6.2 Absorbed dose

rad gray (Gy) 0.01
centigray (cGy) 1

5.6.3 Dose equivalent

rem sievert (sv) 0.01
millisievert (mSv) 10
millirem millisievert (mSv) 0.01
μ?? microsievert (uSv) 10

5.6.4 Exposure (x and gamma rays)

roentgen coulomb per
kilogram (C/kg)
0.000 258


American National Standard for Metric Practice, ANSI/IEEE Std 268-1992, Institute of Electrical and Electronics Engineers, Inc.

Requests for copies should be addressed to the Institute of Electrical and Electronics Engineers (IEEE), Standards Department, 445 Hoes Lane, Piscataway, NJ 08855.

SI Units and Recommendations for the Use of their Multiples and of Certain Other Units, ISO 1000-1992

Requests for copies of this international standard, which is maintained by the International Organization for Standardization (ISO), should be addressed to the American National Standards Institute, 11 West 42nd St., New York, NY 10036.

Standard Practice for Use of the International System of Units (SI) (the Modernized Metric System), ASTM E 380-91 a

Requests for copies should be addressed to the American Society for Testing and Materials (ASTM), 1916 Race Street, Philadelphia, PA 19103.

Rules for SAE Use of SI (Metric) Units, SAE J916 (Rev. May 91)

Requests for copies should be addressed to Society of Automotive Engineers, Inc. (SAE), 400 Commonwealth Drive, Warrendale, PA 15096.

Metric Editorial Guide (fifth edition), ANMC-92-1

Requests for copies should be addressed to the American National Metric Council (ANMc), Publication Services, 301 Warren Ave., Suite 217, Baltimore, MD 21230

Guide to the Use of the Metric System, 1992 edition

Requests for copies should be addressed to the U.S. Metric Association (USMA) 10245 Andasol Ave., Northridge, CA 91325-1504.

The International System of Units (SI), National Institute of Standards and Technology (NIST) Special Publication 330 (1991 Edition)*

Guide for the Use of the International System of Units, The Modernized Metric System, NIST Special Publication 811*

Interpretation of the SI and Metric Conversion Pollcy for Federal Agencies, NIST Special Publication 814*, which includes:

*Requests for copies should be addressed to the National Technical information Service, 5285 Port Royal Rd., Springfield, VA 22161.

Alphabetical Index

absorbed dose
acceleration of gravity
activity (of a radionuclide)
ampere hour
ampere per meter
angle, plane
angle, solid
angular velocity

barrel, oil
board foot
Btu inch per hour square foot
degree Fahrenheit
Btu per degree Fahrenheit
Btu per degree Rankine
Btu per hour
Btu per hour square foot
degree Fahrenheit
Btu per pound
Btu per pound degree Fahrenheit .
Btu per pound degree Rankine . .
Btu per second

candela per square inch
candela per square meter
Celsius tiperature centigray
charge, electric
circular mil
concentration (mass)
conductance, electric
conversion factors
coulomb per kilogram
cubic centimeter
cubic foot
cubic foot per minute
cubic foot per second
cubic inch
cubic meter
cubic meter per second
cubic yard
cubic yard per minute

degree Celsius
degree Fahrenheit
degree Rankine
derived quantities
dose equivalent
dose, absorbed

electric charge
electricity and magnetism
electromagnetic radiation
electromotive force
exposure (x and gamma rays)

field strength, magnetic
flow rate
fluid ounce
flux density, magnetic
flux, luminous
flux, magnetic
foot per second
foot per second squared
foot of water
foot poundforce per second
fuel consumption
fuel efficiency

gallon per day
gallon per minute
gram per liter

heat capacity
heat flow rate
heat transfer
horsepower, electric
horsepower hour

inch of mercury
inch of water
inch per second squared
inertia, moment of
intensity, luminous
intensity, radiant


kilogram meter
kilogram meter per second
kilogram per cubic meter
kilogram square meter
kilojoule per kelvin
kilojoule per kilogram
kilojoule per kilogram kelvin
kilometer per hour
kilometer per liter
kilopoundjorce per square inch

linear expansion coefficient
liter per day
liter per second
lumen per square foot
lumen per square meter
lumen second
luminous exitance
luminous flux
luminous intensity

magnetic field strength
magnetic flux
magnetic flux density
mass, moment of
meter per second
meter per second squared
metric ton
metric ton per cubic meter
mho per centimeter
mil, circular
mile, nautical
mile per gallon
mile per hour
mil(imeter of mercury
millipascal second
moment of force
moment of inertia
moment of mass

nanoohm meter
nautical mile
newton meter

ohm circular mil per foot
ounce, avoirdupois
ounce, fluid
ounce per gallon
ounce, troy

plane angle
potential difference
pound foot
pound foot per second
pound-force foot
pound-force inch
pound-force per square foot
pound-force per square inch
pound per cubic foot
pound per gallon
pound square foot

quantity of electricity
quantity of heat
Quantities of Electricity
Quantities of heat
Quantities of Light
Quantities of Magnetism
Quantities of Mechanics
Quantities of Radiology
Quantities of Space
Quantities of time

radian per second
radiant intensity
radiation, electromagnetic
radionuclide, activity of
reciprocal degree Celsius
reciprocal degree Fahrenheit
reciprocal kelvin
register ton

SI units
siemens per meter
significant digits
solid angle
space and time
specific entropy
specific heat capacity
specific internal energy
square centimeter
square foot
square inch
square kilometer
square meter
square mile
square millimeter
square millimeter per second
square yard
standard acceleration of gravity
standard atmosphere
supplemental lists
survey foot

temperature interval
thermal conductivity
thermodynamic temperature
ton (long)
ton, metric
ton, refrigeration
ton (short)
ton (short) per cubic yard

viscosity (dynamic)
viscosity (kinematic)

watt per meter kelvin
watt per square meter
watt per square meter kelvin
watt per steradian
wan per steradian square meter


1. As used in this standard, “quantity” is the technical word for measurable attributes of phenomena or matter.

2. In commercial and everyday use, and in many technical fields, the term weiqht is usually used as a synonym for mass. This is how 'weight' is used in most United States laws and regulations. See the note at 5.2.1 for further explanation.

3. One or more zeroes at the beginning of a number are not treated as significant.