.Dd $Mdocdate: April 2 2022  $
.Dt SI 7
.Os
.Sh NAME
.Nm SI
.Nd The International System of Units
.Sh SOURCE
NIST SP 330,
.Em The International System of Units (SI) ,
2019 edition,
.Lk https://doi.org/10.6028/NIST.SP.330-2019 .
Some data from the
.Sx NOT-ACCEPTABLE NON-SI UNITS STILL IN USE
section are from NIST SP 811,
.Em NIST Guide for the Use of the International System of Units (SI) ,
2008,
.Lk https://www.nist.gov/pml/special-publication-811 .
.Sh PREFIXES
.TS
allbox tab( );
c | c | c || c | c | c
l c r || l c r.
Name Prefix Power Name Prefix Power
yotta Y 24 yocto y -24
zetta Z 21 zepto z -21
exa E 18 atto a -18
peta P 15 femto f -15
tera T 12 pico p -12
giga G 9 nano n -9
mega M 6 micro \(mc -6
kilo k 3 milli m -3
hecto h 2 centi c -2
deka da 1 deci d -1
.TE
.Sh BASE UNITS
.TS
allbox;
r | l | c | c
r l c c.
Quantity	Unit	Symbol	Dimension
time	second	s	T
length	meter	m	L
kilogram	mass	m	M
current	ampere	A	I
temperature	kelvin	K	\(*H
luminosity	candela	cd	J
Unitless	=	1	=
.TE
Unitless quantities (like indices of refraction) are usually written
with no symbol at all, or with a conventional symbol, like
.Dq rad
(see below).
.Sh DERIVED UNITS
.TS
allbox;
r | l | c | c | c
l l c c c.
Quantity	Unit	Symbol	Base Units	Equivalent
plane angle	radian	rad	m/m	1
solid angle	steradian	sr	m\(S2/m\(S2	1
frequency	hertz	Hz	s⁻¹	=
force	newton	N	kg m s⁻²	=
T{
pressure, stress
T}	pascal	Pa	kg m⁻¹ s⁻²	N m⁻²
T{
energy, work, heat
T}	joule	J	kg m² s⁻²	N m
T{
power, radiant flux
T}	watt	W	kg m² s⁻³	J/s
T{
electric potential difference
T}	volt	V	kg m² s⁻³ A⁻¹	W/A
charge	columb	C	A s	=
capacitance	farad	F	kg⁻¹ m⁻² s⁴ A²	C/V
resistance	ohm	\(*W	kg m² s⁻³ A⁻²	V/A
conductance	siemens	S	kg⁻¹ m⁻² s³ A²	A/V
T{
magnetic flux
T}	weber	Wb	kg m² s⁻² A⁻¹	V s
T{
magnetic flux density
T}	tesla	T	kg s⁻² A⁻¹	Wb m⁻²
inductance	henry	H	kg m² s⁻² A⁻²	Wb/A
T{
temperature, celsius
T}	celsius	\(de C	K + 273.15	=
T{
luminous flux
T}	lumen	lm	cd sr	=
T{
illuminance
T}	lux	cd sr m⁻²	lm m⁻²
T{
activity referred to a
radionuclide
T}	becquerel	Bq	s⁻¹	=
T{
absorbed dose, kerma
T}	gray	m² s⁻²	J/kg
T{
dose equivalent
T}	sievert	Sv	m² s⁻²	J/kg
T{
catalytic activity
T}	katal	kat	mol s⁻¹	=
.TE
The equivalent units for pressure do not appear in the source.
.Sh SAMPLE OF OTHER DERIVED UNITS
.TS
allbox;
l r r.
Quantity	Units	Base
dynamic viscosity	Pa s	kg m⁻¹ s⁻¹
surface tension	N m	kg m² s⁻²
T{
angular velocity, angular frequency
T}	rad s⁻¹	s⁻¹
T{
heat flux density, irradiance
T}	W m⁻²	kg s⁻³
T{
heat capacity, entropy
T}	J K⁻¹	kg m² s⁻² K⁻¹
T{
specific heat capacity, specific entropy
T}	J K⁻¹ kg⁻¹	m² s⁻² K⁻¹
T{
thermal conductivity
T}	W m⁻¹ K⁻¹	kg m s⁻³ K⁻¹
T{
electric field strength
T}	V m⁻¹	kg m⁻¹ s⁻³ A⁻¹
permittivity	F m⁻¹	kg⁻¹ m⁻³ s⁴ A²
permeability	H m⁻¹	kg m s⁻² A⁻²
T{
radiant intensity
T}	W sr⁻¹	kg m² s⁻³
radiance	W sr⁻¹ m⁻²	kg s⁻³
.TE
The source gives more examples.
.Sh NON-SI UNITS ACCEPTED FOR USE IN SI
.TS
allbox;
l l c r.
Quantity	Name	Sym.	Value
time	minute	min	1 min = 60 s
\^	hour	h	1 h = 60 min = 3600 s
\^	day	d	1 d = 24 h = 86400 s
length	T{
astronomical unit
T}	au	T{
1 au = 149 597 870 700 m
T}
angle	degree	\(de	1\(de = (\(*p/180) rad
\^	minute	\(fm	T{
1\(fm = (1/60)\(de = (\(*p/10 800) rad
T}
\^	second	\(sd	T{
1\(sd = (1/60)\(de = (\(*p/648 000) rad
T}
area	hectare	ha	1 ha = 1 hm² = 10⁴ m²
volume	liter	L	1 L = 1 dm³ = 10³ cm³ = 10⁻³ m³
mass	metric ton	t	1 t = 10³ kg
\^	dalton	Da	1 Da = 1.660 539 040 (20) E-27 kg
energy	electronvolt	eV	1 eV = 1.602 176 634 e-19 J
T{
logarithmic quantities
T}	neper	Np	natural log
\^	bel	B	base-10 log
\^	decibel	dB	1 dB = 10⁻¹ B
.TE
.Sh NOT-ACCEPTABLE NON-SI UNITS STILL IN USE
.TS
allbox;
l l c r.
Quantity	Name	Sym.	Value
length	ångström	\(oA	10⁻¹⁰ m
\^	micron	\(*m	1 \(*mm
\^	parsec	pc	1 pc = 3.085 678E+16 m
T{
radiation dose
T}	rad	rad OR rd	1 rd = 10⁻² Gy
pressure	T{
millimeter of mercury
T}	mmHg	1 mmHg \(=~ 133.322 Pa
T{
magnetic flux density
T}	gauss	G OR Gs	1 G = 100 μT
.TE
.Sh INFO
This file is public domain. Manual page version 1.0.