path: root/si.7

.Dd $Mdocdate: May 22 2024  $
.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 .

The IEC binary prefixes are defined in ISO/IEC 80000-13.
.Sh PREFIXES
.TS
allbox tab( );
c | c | c || c | c | c
l c r || l c r.
Name Prefix Power Name Prefix Power
quetta Q 30 quecto q -30
ronna R 27 ronto r -27
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 BINARY PREFIXES
Binary prefixes multiply a unit by a power of 2. They not a part of the
SI system. Most people will say
.Dq kilobyte
instead of
.Dq kibibyte ,
.Dq megabyte
instead of
.Dq mebibyte ,
and so on. Mac OSX and Linux utilities commonly report
units using the binary prefixes
(
.Dq KiB ,
.Dq MiB ,
etc).
.TS
allbox tab( );
c | c | c
l c r.
Name Prefix Power Related
kibi Ki 10 kilo
mebi Mi 20 mega
gibi Gi 30 giga
tebi Ti 40 tera
pebi Pi 50 peta
exbi Ei 60 exa
zebi Zi 70 zetta
yobi Yi 80 yotta
.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 sources give 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 2024.01.