Federal Register notice of December 20, 1990, 55 FR 52242-52245
Interpretation of the International System of Units for the United
States
Tables
TABLE 1a. SI Base Units
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SI Unit
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Quantity Name Symbol
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length.........................meter..........................m
mass1..........................kilogram.......................kg
time...........................second.........................s
electric current...............ampere.........................A
thermodynamic temperature......kelvin.........................K
amount of substance............mole...........................mol
luminous intensity.............candela........................cd
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1``Weight'' in common parlance is often used to mean ``mass.''
TABLE 1b. SI Supplementary Units
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SI Unit
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Expression
Quantity Name Symbol in terms of
SI base units
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plane angle....................radian........................rad........m·m-1=1
solid angle....................steradian.....................sr.........m2·m-2=1
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TABLE 2. Examples of SI Derived Units Expressed in Terms of Base Units
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SI Unit
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Quantity Name Symbol
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area..........................square meter...................m2
volume........................cubic meter....................m3
speed, velocity...............meter per second...............m/s
acceleration..................meter per second squared.......m/s2
wave number...................reciprocal meter...............m-1
density, mass density.........kilogram per cubic meter.......kg/m3
specific volume...............cubic meter per kilogram.......m3/kg
current density...............ampere per square meter........A/m2
magnetic field strength.......ampere per meter...............A/m
concentration
(of amount of substance)....mole per cubic meter...........mol/m3
luminance.....................candela per square meter.......cd/m2
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TABLE 3. SI Derived Units with Special Names
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SI Unit
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Expression
Quantity Name Symbol in terms of
other units
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frequency.....................hertz..........................Hz.........s-1
force.........................newton.........................N..........m·kg/s2
pressure,stress...............pascal.........................Pa.........N/m2
energy,work,quantity of heat..joule..........................J..........N·m
power, radiant flux...........watt...........................W..........J/s
electric charge,
quantity of electricity....coulomb........................C..........s·A
electric potential,
potential difference,
electromotive force........volt ..........................V..........W/A
capacitance...................farad..........................F..........C/V
electric resistance...........ohm............................
..........V/A
electric conductance..........siemens .......................S..........A/V
magnetic flux.................weber..........................Wb.........V·s
magnetic flux density.........tesla..........................T..........Wb/m2
inductance....................henry..........................H..........Wb/A
Celsius temperature1..........degree Celsius.................°C.........K
luminous flux.................lumen..........................lm.........cd·sr
illuminance ..................lux............................lx.........lm/m2
activity (of a radionuclide)..becquerel......................Bq.........s-1
absorbed dose,
specific energy imparted,
kerma, absorbed dose index..gray...........................Gy.........J/kg
dose equivalent,
dose equivalent index.......sievert........................Sv.........J/kg
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1In addition to the thermodynamic temperature (symbol T) expressed in kelvins (see Table 1a), use is also made of Celsius
temperature (symbol t) defined by the equation t=T-To where To=273.15 K by definition. To express Celsius temperature, the unit
``degree Celsius'' which is equal to the unit ``kelvin'' is used;
in this case, ``degree Celsius'' is a special name used in place
of ``kelvin.'' An interval or difference of Celsius temperature
can, however, be expressed in kelvins as well as in degrees Celsius.
TABLE 4. Examples of SI Derived Units Expressed by Means of Special Names
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SI Unit
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Quantity Name Symbol
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dynamic viscosity...............pascal second..............Pa·s
moment of force.................newton meter...............N·m
surface tension.................newton per meter...........N/m
heat flux density, irradiance...watt per square meter......W/m2
heat capacity, entropy..........joule per kelvin...........J/K
specific heat capacity,
specific entropy..............joule per kilogram kelvin..J(kg·K)
specific energy.................joule per kilogram.........J/kg
thermal conductivity............watt per meter kelvin......W/(m·K)
energy density..................joule per cubic meter......J/m3
electric field strength.........volt per meter.............V/m
electric charge density.........coulomb per cubic meter....C/m3
electric flux density...........coulomb per square meter...C/m2
permittivity....................farad per meter............F/m
permeability....................henry per meter............H/m
molar energy....................joule per mole.............J/mol
molar entropy,
molar heat capacity...........joule per mole kelvin......J/(mol·K)
exposure (x and 
rays).........coulomb per kilogram.......C/kg
absorbed dose rate..............gray per second............Gy/s
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TABLE 5. Examples of SI Derived Units Formed by Using Supplementary Units
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SI Unit
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Quantity Name Symbol
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angular velocity................radian per second..........rad/s
angular acceleration............radian per second squared..rad/s 2
radiant intensity...............watt per steradian.........W/sr
radiance........................watt per square meter
steradian................W/(m2·sr)
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TABLE 6. SI Prefixes
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Factor Prefix Symbol
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1018..............................exa........................E
1015..............................peta.......................P
1012..............................tera.......................T
109...............................giga.......................G
106...............................mega.......................M
103...............................kilo.......................k
102...............................hecto......................h
101...............................deka.......................da
10-1..............................deci.......................d
10-2..............................centi......................c
10-3..............................milli......................m
10-6..............................micro......................µ
10-9..............................nano.......................n
10-12.............................pico.......................p
10-15.............................femto......................f
10-18.............................atto.......................a
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TABLE 7. Units in Use With the International System
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Name Symbol Value in SI unit
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minute (time).....................min......................1 min=60 s
hour..............................h........................1 h=60 min=3 600 s
day...............................d........................1 d=24 h=86 400 s
degree (angle)....................°........................1°=( 
/180) rad
minute (angle)....................
........................1=(1/60)°=(/10 800) rad
second (angle)............................................1=(1/60)=(/648 000) rad
1liter............................L........................1 L=1 dm3=10-3 m3
2metric ton.......................t........................1 t=103 kg
hectare (land area)...............ha.......................1 ha=1 hm2=104 m2
3electronvolt.....................eV.......................1 eV=1.602 18?10-19 J,
approximately
3unified atomic mass unit.........u........................1 u=1.660 54?10-27 kg,
approximately
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1Both L and l are internationally accepted symbols for liter. Because
``l'' can easily be confused with the numeral ``1,'' the symbol
"L" is recommended for United States use.
2In many countries, this unit is called ``tonne.''
3The values of these units expressed in terms of SI units must
be obtained by experiment, and are therefore not known exactly.
The electronvolt is the kinetic energy acquired by an electron
passing through a potential difference of 1 volt in vacuum. The
unified atomic mass unit is equal to (1/12) of the mass of the
atom of the nuclide 12C.
TABLE 8. Units in Use Temporarily with the International System
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nautical mile barn roentgen
knot bar rad3
ångström gal2 rem4
are1 curie
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1Unit of land area.
2Unit of acceleration.
3Unit of absorbed dose.
4Unit of dose equivalent.
Note 1 Table.
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Factor Prefix Symbol
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1024.............................yotta.......................Y
1021.............................zetta.......................Z
10-21............................zepto.......................z
10-24............................yocto.......................y
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