List of conversion factors explained

This article gives a list of conversion factors for several physical quantities. A number of different units (some only of historical interest) are shown and expressed in terms of the corresponding SI unit. Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10⁻⁶ metre). Within each table, the units are listed alphabetically, and the SI units (base or derived) are highlighted.

The following quantities are considered: length, area, volume, plane angle, solid angle, mass, density, time, frequency, velocity, volumetric flow rate, acceleration, force, pressure (or mechanical stress), torque (or moment of force), energy, power (or heat flow rate), action, dynamic viscosity, kinematic viscosity, electric current, electric charge, electric dipole, electromotive force (or electric potential difference), electrical resistance, capacitance, magnetic flux, magnetic flux density, inductance, temperature, information entropy, luminous intensity, luminance, luminous flux, illuminance, radiation.

Legend! Symbol! Definition
≡	exactly equal
≈	approximately equal to
≘	(exactly) corresponds to (different types of quantity describing the same phenomenon)
	indicates that `digits` repeat infinitely (e.g. corresponds to)
(H)	of chiefly historical interest

Length

Length!Name of unit!Symbol!Definition!Relation to SI units
	Å	≡	≡ 0.1 nm
	au	≡ ≈ Distance from Earth to Sun	≡ ^[1]
	am	≡	≡
barleycorn (H)		= in (see note above about rounding)	= 8.4 m
	a₀	= Bohr radius of hydrogen	≈ ^[2]
cable length (imperial)		≡ 608 ft	≈ 185.3184 m
cable length (International)		≡ nmi	≡ 185.2 m
cable length (US)		≡ 720 ft	= 219.456 m
chain (Gunter's; Surveyor's)	ch	≡ 66 ft (US) ≡ 4 rods^[3]	≈
cubit (H)		≡ Distance from fingers to elbow ≈ 18 in	≈ 0.5 m
ell (H)	ell	≡ 45 in ^[4] (In England usually)	= 1.143 m
	ftm	≡ 6 ft	= 1.8288 m
	fm	≡	≡
	fm	≡	≡
finger		≡ in	=
finger (cloth)		≡ in	= 0.1143 m
foot (Benoît) (H)	ft (Ben)		≈
foot (Cape) (H)		Legally defined as 1.033 English feet in 1859	≈
foot (Clarke's) (H)	ft (Cla)		≈
foot (Indian) (H)	ft Ind		≈
	mf	≡ 300 mm	≡ 0.3 m
foot, metric (Mesures usuelles) (H)		≡ m	≡ 0. m
foot (International)	ft	≡ 0.3048 m ≡ yd ≡ 12 inches	≡ 0.3048 m
foot (Sear's) (H)	ft (Sear)		≈
foot (US Survey)	ft (US)	≡ m ^[5]	≈
french charriere	F	≡ mm	= 0. m
	fur	≡ 10 chains = 660 ft = 220 yd	= 201.168 m
		≡ 4 in	≡ 0.1016 m
inch (International)	in	≡ 2.54 cm ≡ yd ≡ ft	≡ 0.0254 m
league (land)	lea	≈ 1 hour walk, Currently defined in US as 3 Statute miles, but historically varied from 2 to 9 km	≈
		≡ 24 light-hours	≡
		≡ 60 light-minutes	≡
		≡ 60 light-seconds	≡
		≡ Distance light travels in one second in vacuum	≡
	ly	≡ Distance light travels in vacuum in 365.25 days ^[6]	≡
	ln	≡ in ^[7]	= m
link (Gunter's; Surveyor's)	lnk	≡ ch ≡ 0.66 ft (US) ≡ 7.92 in	≈
link (Ramsden's; Engineer's)	lnk	≡ 1 ft	= 0.3048 m
metre (SI base unit) (meter)	m	≡ Distance light travels in of a second in vacuum.	(SI base unit)
mickey		≡ in	=
micrometre (old: micron)	μ; μm	≡	≡
	mil	≡	=
mil (Sweden and Norway)	mil	≡ 10 km	=
mile (geographical) (H)		≡	=
mile (international)	mi	≡ 80 chains ≡ ≡	≡
mile (tactical or data)		≡	≡
mile (telegraph) (H)	mi	≡	=
mile (US Survey)	mi	≡ US Survey feet ≡ (×) m	≈
nail (cloth)		≡ in	=
	nm	≡	≡
nautical league	NL; nl	≡ 3 nmi	=
nautical mile (Admiralty)	NM (Adm); nmi (Adm)	=	=
nautical mile (international)	NM; nmi	≡ ^[8]	≡
nautical mile (US pre 1954)		≡ 1853.248 m	≡ 1853.248 m
pace		≡ 2.5 ft	= 0.762 m
		≡ 3 in	= 0.0762 m
	pc	Distant point with a *parallax shift of one arc sec*ond from a base of one astronomical unit. ≡ au^[9] ^[10]	≈ ^[11]
		≡ 12 points	Dependent on point measures.
	pm	≡	≡
point (American, English)^[12] ^[13]	pt	≡ in	≈
point (Didot; European) ^[14]	pt	≡ × of pied du roi; After 1878: ≡ cm	≈ ; After 1878: ≈
point (PostScript)	pt	≡ in	= m
point (TeX)	pt	≡ in	= 0.00 m
quarter		≡ yd	= 0.2286 m
rod pole; perch (H)	rd	≡ ft	= 5.0292 m
rope (H)	rope	≡ 20 ft	= 6.096 m
shaku (Japan)		≡ 10/33 m	≈ 0.303 0303 m
span (H)		≡ 9 in	= 0.2286 m
			≡
stick (H)		≡ 2 in	= 0.0508 m
toise (French, post 1667) (H)	T	≡ 27000/13853 m	≈ 1.949 0363 m
	twp	≡ in	= 1.763 m
x unit siegbahn	xu		≈ m
yard (International)	yd	≡ 0.9144 m ≡ 3 ft ≡ 36 in	≡ 0.9144 m
	ym	≡	≡
	zm	≡	≡

Area

Area!Name of unit!Symbol!Definition!Relation to SI units
acre (international)	ac	≡ =	≡
acre (US survey)	ac	≡ 10 sq ch =, also	≈ ^[15]
	a	≡ 100 m²	≡ 100 m²
	b	≡ 10⁻²⁸ m²	≡ 10⁻²⁸ m²
barony		≡ ac	≡
board	bd	≡	≡
boiler horsepower equivalent direct radiation	bhp EDR	≡ 1 ft² × 1 bhp / (240 BTU_IT/h)	≈
	circ in	≡ sq in	≈
circular mil; circular thou	circ mil	≡ mil²	≈
cord		≡ 192 bd	≡
cuerda (PR Survey)	cda	≡ 1 cda x 1 cda = acre	≡
		≡	≡
guntha (India)		≡ 121 sq yd	≈ 101.17 m²
	ha	≡	≡
		≈ 120 ac (variable)	≈
rood	ro	≡ ac	=
		≡ m × m	≈
section		≡	=
		≡ 10⁻⁵² m²	= 10⁻⁵² m²
square (roofing)		≡	=
square chain (international)	sq ch	≡ = ac	≡
square chain (US Survey)	sq ch	≡ = US survey acre	≈
	sq ft	≡	≡
square foot (US Survey)	sq ft	≡	≈
	sq in	≡	≡
	km²	≡ 1 km × 1 km	= 10⁶ m²
square link (Gunter's)(International)	sq lnk	≡ 1 lnk × 1 lnk ≡ 0.66 ft × 0.66 ft	=
square link (Gunter's)(US Survey)	sq lnk	≡ ≡	≈
square link (Ramsden's)	sq lnk	≡ 1 lnk × 1 lnk ≡ 1 ft × 1 ft	=
square metre (SI unit)	m²	≡ 1 m × 1 m	= 1 m²
square mil; square thou	sq mil	≡ 1 mil × 1 mil	=
	sq mi	≡ 1 mi × 1 mi	≡
square mile (US Survey)	sq mi	≡ 1 mi (US) × 1 mi (US)	≈
square rod/pole/perch	sq rd	≡ 1 rd × 1 rd	=
square yard (International)	sq yd	≡ 1 yd × 1 yd	≡
		≡	=
		≡ 36 sq mi (US)	≈
		≈ 30 ac	≈

Volume

Volume!Name of unit!Symbol!Definition!Relation to SI units
	ac ft	≡ 1 ac x 1 ft =	=
acre-inch		≡ 1 ac × 1 in	=
barrel (imperial)	bl (imp)	≡ 36 gal (imp)	=
barrel (petroleum); archaic blue-barrel	bl; bbl	≡ 42 gal (US)	≡
barrel (US dry)	bl (US)	≡ 105 qt (US) = 105/32 bu (US lvl)	=
barrel (US fluid)	fl bl (US)	≡ gal (US)	=
	bdft	≡ 144 cu in	≡
bucket (imperial)	bkt	≡ 4 gal (imp)	=
bushel (imperial)	bu (imp)	≡ 8 gal (imp)	=
bushel (US dry heaped)	bu (US)	≡ bu (US lvl)	=
bushel (US dry level)	bu (US lvl)	≡	=
butt, pipe		≡ 126 gal (US) (wine)	=
		≡ 4 bu (imp)	=
cord (firewood)		≡	=
cord-foot		≡ 16 cu ft	=
	cu fm	≡ 1 fm × 1 fm × 1 fm	=
	ft³	≡ 1 ft × 1 ft × 1 ft	≡
	in³	≡ 1 in × 1 in × 1 in	≡
cubic metre (SI unit)	m³	≡ 1 m × 1 m × 1 m	≡ 1 m³
	cu mi	≡ 1 mi × 1 mi × 1 mi	≡
	yd³	≡ 27 cu ft	≡
cup (breakfast)		≡ 10 fl oz (imp)	=
cup (Canadian)	c (CA)	≡ 8 fl oz (imp)	=
cup (metric)	c	≡	≡
cup (US customary)	c (US)	≡ 8 US fl oz ≡ gal (US)	=
cup (US food nutrition labeling)	c (US)	≡ 240 mL	=
dash (imperial)		≡ gi (imp) = 1/8 tsp (imp)	= m³
dash (US)		≡ US fl oz = 1/8 US tsp	=
dessertspoon (imperial)		≡ gi (imp)	= m³
drop (imperial)	gtt	≡ fl oz (imp)	= m³
drop (imperial) (alt)	gtt	≡ gi (imp)	≈
drop (medical)		≡ mL	= 83. m³
drop (metric)		≡ mL	=
drop (US)	gtt	≡ US fl oz	= m³
drop (US) (alt)	gtt	≡ US fl oz	≈
drop (US) (alt)	gtt	≡ US fl oz	≈
fifth		≡ US gal	=
		≡ 9 gal (imp)	=
fluid drachm (imperial)	fl dr	≡ fl oz (imp)	=
fluid dram (US); US fluidram	fl dr	≡ US fl oz	=
fluid scruple (imperial)	fl s	≡ fl oz (imp)	= m³
gallon (beer)	beer gal	≡ 282 cu in	=
gallon (imperial)	gal (imp)	≡	≡
gallon (US dry)	gal (US)	≡ bu (US lvl)	=
gallon (US fluid; Wine)	gal (US)	≡ 231 cu in	≡
gill (imperial); Noggin	gi (imp); nog	≡ 5 fl oz (imp)	=
gill (US)	gi (US)	≡ 4 US fl oz	=
hogshead (imperial)	hhd (imp)	≡ 2 bl (imp)	=
hogshead (US)	hhd (US)	≡ 2 fl bl (US)	=
		≡ US fl oz	≈
		≡ 18 gal (imp)	=
	λ	≡ 1 mm³	=
		≡ 80 bu (imp)	=
litre (liter)	L or l	≡ 1 dm³ ^[16]	≡ 0.001 m³
load		≡ 50 cu ft	=
minim (imperial)	min	≡ fl oz (imp) = 1/60 fl dr (imp)	= m³
minim (US)	min	≡ US fl oz = US fl dr	=
ounce (fluid imperial)	fl oz (imp)	≡ gal (imp)	≡
ounce (fluid US customary)	US fl oz	≡ gal (US)	≡
ounce (fluid US food nutrition labeling)	US fl oz	≡ 30 mL	≡
peck (imperial)	pk	≡ 2 gal (imp)	=
peck (US dry)	pk	≡ US lvl bu	=
	per	≡	=
pinch (imperial)		≡ gi (imp) = dash (imp)	= m³
pinch (US)		≡ US fl oz = US dash	=
pint (imperial)	pt (imp)	≡ gal (imp)	=
pint (US dry)	pt (US dry)	≡ bu (US lvl) ≡ gal (US dry)	=
pint (US fluid)	pt (US fl)	≡ gal (US)	=
pony		≡ US fl oz	=
pottle; quartern		≡ gal (imp) = 80 fl oz (imp)	=
quart (imperial)	qt (imp)	≡ gal (imp)	=
quart (US dry)	qt (US)	≡ bu (US lvl) = gal (US dry)	=
quart (US fluid)	qt (US)	≡ gal (US fl)	=
quarter; pail		≡ 8 bu (imp)	=
register ton		≡ 100 cu ft	=
sack (US)		≡ 3 bu (US lvl)	=
seam		≡ 8 bu	=
shot (US)		usually 1.5 US fl oz	≈
strike (imperial)		≡ 2 bu (imp)	=
strike (US)		≡ 2 bu (US lvl)	=
tablespoon (Australian metric)			≡
tablespoon (Canadian)	tbsp	≡ fl oz (imp)	=
tablespoon (imperial)	tbsp	≡ fl oz (imp)	=
tablespoon (metric)			≡
tablespoon (US customary)	tbsp	≡ US fl oz	=
tablespoon (US food nutrition labeling)	tbsp	≡ 15 mL	=
teaspoon (Canadian)	tsp	≡ fl oz (imp)	= m³
teaspoon (imperial)	tsp	≡ gi (imp)	= m³
teaspoon (metric)		≡	≡
teaspoon (US customary)	tsp	≡ US fl oz	=
teaspoon (US food nutrition labeling)	tsp	≡ 5 mL	=
		≡ 1 cu ft	=
ton (displacement)		≡ 35 cu ft	=
ton (freight)		≡ 40 cu ft	=
ton (water)		≡ 28 bu (imp)	=
		≡ 252 gal (wine)	=
wey (US)		≡ 40 bu (US lvl)	=

Plane angle

Plane angle!Name of unit!Symbol!Definition!Relation to SI units
	(various)	≡ rad	≈
		≡ rad	≈
	mrad	≡ rad	≈
		≡ rad	≈
arcminute MOA	'	≡	≈
	"	≡	≈
	'	≡ grad	≈
	"	≡ grad	≈
	°	≡ of a revolution ≡ rad	≈
grad gradian; gon	grad	≡ of a revolution ≡ rad ≡ 0.9°
		≡ 45°	≈
		≡ 90°	≈
radian (SI unit)	rad	The angle subtended at the center of a circle by an arc whose length is equal to the circle's radius. One full revolution encompasses 2π radians.	= 1 rad
sextant		≡ 60°	≈
sign		≡ 30°	≈

Solid angle

Solid angle!Name of unit!Symbol!Definition!Relation to SI units
		– The solid angle subtended by a sphere at its centre.
	deg²; sq.deg.; (°)²
steradian (SI unit)	sr	The solid angle subtended at the center of a sphere of radius r by a portion of the sphere having an area r². A sphere subtends 4π sr.	= 1 sr

Mass

Notes:

See Weight for detail of mass/weight distinction and conversion.
Avoirdupois is a system of mass based on a pound of 16 ounces, while Troy weight is the system of mass where 12 troy ounces equals one troy pound.
The symbol is used to denote standard gravity in order to avoid confusion with the (upright) g symbol for gram.

Mass!Name of unit!Symbol!Definition!Relation to SI units
	u; AMU	Same as dalton (see below)	≈
atomic unit of mass, electron rest mass	m_e		≈ ^[17]
bag (coffee)		≡ 60 kg	= 60 kg
bag (Portland cement)		≡ 94 lb av	=
barge		≡ short ton	=
	kt	≡ gr	= mg
carat (metric)	ct	≡ 200 mg	= 200 mg
		≡ 8 lb av	=
crith		≡ mass of 1 L of hydrogen gas at STP	≈ 89.9349 mg
	Da	1/12 the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest	≈
dram (apothecary; troy)	dr t	≡ 60 gr	=
dram (avoirdupois)	dr av	≡ gr	=
	eV/c²	≡ 1 eV / c²	=
gamma	γ	≡ 1 μg	= 1 μg
	gr	≡ lb av	≡
	gv	grave was the original name of the kilogram	≡ 1 kg
hundredweight (long)	long cwt or cwt	≡ 112 lb av	=
hundredweight (short); cental	sh cwt	≡ 100 lb av	=
hyl metric slug		≡ 1 kgf / 1 m/s²	=
kilogram (kilogramme)	kg	≈ mass of the prototype near Paris ≈ mass of 1 litre of water	(SI base unit)
	kip	≡ av	=
		≡ 8 oz t	=
mite		≡ gr	=
mite (metric)		≡ g	= 50 mg
	oz t	≡ lb t	=
ounce (avoirdupois)	oz av	≡ lb	=
ounce (US food nutrition labelling)	oz	≡ 28 g	= 28 g
	dwt; pwt	≡ oz t	=
		≡ ct	= 2 mg
	lb av	≡ = grains	≡
		≡ 500 g	= 500 g
	lb t	≡ grains	=
quarter (imperial)		≡ long cwt = 2 st = 28 lb av	=
quarter (informal)		≡ short ton	=
quarter, long (informal)		≡ long ton	=
quintal (metric)	q	≡ 100 kg	= 100 kg
scruple (apothecary)	s ap	≡ 20 gr	=
sheet		≡ lb av	= 647.9891 mg
slug geepound	slug	≡ × 1 lb av × 1 s²/ft	≈
	st	≡ 14 lb av	=
ton, assay (long)	AT	≡ 1 mg × 1 long ton ÷ 1 oz t	= 32. g
ton, assay (short)	AT	≡ 1 mg × 1 short ton ÷ 1 oz t	= 29.1 g
ton, long	long tn or ton	≡	=
	sh tn	≡	=
tonne (mts unit)	t	≡	=
		≡ 252 lb = 18 st	= (variants exist)
zentner	Ztr.	Definitions vary.^[18]

Density

Density!Name of unit!Symbol!Definition!Relation to SI units
gram per millilitre	g/mL	≡ g/mL	=
kilogram per cubic metre (SI unit)	kg/m³	≡ kg/m³	= 1 kg/m³
kilogram per litre	kg/L	≡ kg/L	=
ounce (avoirdupois) per cubic foot	oz/ft³	≡ oz/ft³	≈
ounce (avoirdupois) per cubic inch	oz/in³	≡ oz/in³	≈
ounce (avoirdupois) per gallon (imperial)	oz/gal	≡ oz/gal	≈
ounce (avoirdupois) per gallon (US fluid)	oz/gal	≡ oz/gal	≈
pound (avoirdupois) per cubic foot	lb/ft³	≡ lb/ft³	≈
pound (avoirdupois) per cubic inch	lb/in³	≡ lb/in³	≈
pound (avoirdupois) per gallon (imperial)	lb/gal	≡ lb/gal	≈
pound (avoirdupois) per gallon (US fluid)	lb/gal	≡ lb/gal	≈
slug per cubic foot	slug/ft³	≡ slug/ft³	≈

Time

Time!Name of unit!Symbol!Definition!Relation to SI units
	a.u.	≡ a₀/(α⋅c)	≈
		≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d	= or ^[19]
	c	≡ 100 years (100 a)	= ^[20] ^[21]
	d	= 24 h = min	=
day (sidereal)	d	≡ Time needed for the Earth to rotate once around its axis, determined from successive transits of a very distant astronomical object across an observer's meridian (International Celestial Reference Frame)	≈
	dec	≡ 10 years (10 a)	=
	fn	≡ 2 wk	=
		≡ h	= 3. s
		≡ 4 Callippic cycles - 1 d	=
	h	≡ 60 min	=
	j	≡ s	= 16. ms
jiffy (alternative)	ja	≡ s	= 10 ms
kè (quarter of an hour)		≡ h = d = 15 min	= 900 s
kè (traditional)		≡ d = 14.4 min	= 864 s
lustre; lūstrum		≡ 5 a of 365 d^[22]	=
Metonic cycle enneadecaeteris		≡ 110 mo (hollow) + 125 mo (full) = 6940 d ≈ 19 a	=
		≡ years	=
	md	≡ d	= 86.4 s
	min	≡ 60 s, due to leap seconds sometimes 59 s or 61 s,	= 60 s
		≡ 90 s	= 90 s
month (full)	mo	≡ 30 d^[23]	=
month (Greg. av.)	mo	=	≈
month (hollow)	mo	≡ 29 d	=
Month (synodic)	mo	Cycle time of moon phases ≈ (average)	≈
		= 48 mo (full) + 48 mo (hollow) + 3 mo (full) = 8 a of 365.25 d = 2922 d	=
		≡	≈ ^[24]
second (SI base unit)	s	≡ Time of periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at 0 K (but other seconds are sometimes used in astronomy). Also that time it takes for light to travel a distance of metres.	(SI base unit)
		≡ 10⁻⁸ s	= 10 ns
sigma		≡ 10⁻⁶ s	= 1 μs
		≡ a of 365 d	=
	S	≡ 10⁻¹³ s	= 100 fs
	wk	≡ 7 d = 168 h =	=
year (common)		365 d	= ^[25]
year (Gregorian)	a, y, or yr	= 365.2425 d average, calculated from common years (365 d) plus leap years (366 d) on most years divisible by 4. See leap year for details.	=
year (Julian)	a, y, or yr	= 365.25 d average, calculated from common years (365 d) plus one leap year (366 d) every four years	=
year (leap)	a, y, or yr	366 d	=
	a, y, or yr	Conceptually, the length of time it takes for the Sun to return to the same position in the cycle of seasons, ^[26] approximately d, each day being SI seconds^[27]	≈
	a, y, or yr	≡ Time taken for Sun to return to the same position with respect to the stars of the celestial sphere, approximately	≈
Notes:

Frequency

Frequency!Name of unit!Symbol!Definition!Relation to SI units
actions per minute	APM	≡ 1/60 Hz	≈
	cps	≡ 1 Hz	= 1 cps = 1 Hz
degree per second	deg/s	≡ 1 °/s ≡ 1/360 Hz	= Hz
hertz (SI unit)	Hz	≡ One cycle per second	= 1 Hz = 1/s
	rad/s	≡ 1/(2π) Hz	≈
	rpm	≡ One rpm equals one rotation completed around a fixed axis in one minute of time.	≈

Speed or velocity

Definition!Relation to SI units
	fph	≡ 1 ft/h	= 8.4 m/s
	fpm	≡ 1 ft/min	=
	fps	≡ 1 ft/s	=
		≡ furlong/fortnight	≈
	iph	≡ 1 in/h	= 7.0 m/s
	ipm	≡ 1 in/min	= 4.2 m/s
	ips	≡ 1 in/s	=
	km/h	≡ 1 km/h	= 2. m/s
	kn	≡ 1 nmi/h = 1.852 km/h	= 0.51 m/s
knot (Admiralty)	kn	≡ 1 NM (Adm)/h = ^[28]	= m/s
	M	Ratio of the speed to the speed of sound in the medium (unitless).	≈ 340 m/s in air at sea level ≈ 295 m/s in air at jet altitudes
metre per second (SI unit)	m/s	≡ 1 m/s	= 1 m/s
	mph	≡ 1 mi/h	=
	mpm	≡ 1 mi/min	=
	mps	≡ 1 mi/s	=
speed of light in vacuum	c	≡	=
speed of sound in air	s	to (761-)	≈
Note

A velocity consists of a speed combined with a direction; the speed part of the velocity takes units of speed.

Flow (volume)

Volumetric flow rate!Name of unit!Symbol!Definition!Relation to SI units
cubic foot per minute	CFM	≡ 1 ft³/min	=
cubic foot per second	ft³/s	≡ 1 ft³/s	=
cubic inch per minute	in³/min	≡ 1 in³/min	= m³/s
cubic inch per second	in³/s	≡ 1 in³/s	=
cubic metre per second (SI unit)	m³/s	≡ 1 m³/s	= 1 m³/s
gallon (US fluid) per day	GPD	≡ 1 gal/d	= m³/s
gallon (US fluid) per hour	GPH	≡ 1 gal/h	= m³/s
gallon (US fluid) per minute	GPM	≡ 1 gal/min	=
litre per minute	l/min or L/min	≡ 1 L/min	= 1. m³/s

Acceleration

Acceleration!Name of unit!Symbol!Definition!Relation to SI units
	fph/s	≡ 1 ft/(h⋅s)	= 8.4 m/s²
	fpm/s	≡ 1 ft/(min⋅s)	=
foot per second squared	fps²	≡ 1 ft/s²	=
gal galileo	Gal	≡ 1 cm/s²	= 10⁻² m/s²
	ipm/s	≡ 1 in/(min⋅s)	= 4.2 m/s²
inch per second squared	ips²	≡ 1 in/s²	=
	kn/s	≡ 1 kn/s	≈ 5.1 m/s²
metre per second squared (SI unit)	m/s²	≡ 1 m/s²	= 1 m/s²
	mph/s	≡ 1 mi/(h⋅s)	=
	mpm/s	≡ 1 mi/(min⋅s)	= 26.8224 m/s²
mile per second squared	mps²	≡ 1 mi/s²	=
		≡	=

Force

Definition!Relation to SI units
		≡	≈ ^[29]
dyne (CGS unit)	dyn	≡ g⋅cm/s²	= 10⁻⁵ N
kilogram-force kilopond; grave-force	kgf; kp; gvf	≡ × 1 kg	=
kip kip-force	kip; kipf; klbf	≡ ×	=
milligrave-force, gravet-force	mgvf; gvtf	≡ × 1 g	=
long ton-force	tnf	≡ × 1 long ton	=
newton (SI unit)	N	A force capable of giving a mass of one kilogram an acceleration of one metre per second per second.	= 1 N = 1 kg⋅m/s²
	ozf	≡ × 1 oz	=
	lbf	≡ × 1 lb	=
	pdl	≡ 1 lb⋅ft/s²	=
short ton-force	tnf	≡ × 1 short ton	=
sthene (mts unit)	sn	≡ 1 t⋅m/s²	= 10³ N

Pressure or mechanical stress

Pressure!Name of unit!Symbol!Definition!Relation to SI units
atmosphere (standard)	atm		≡ ^[30]
atmosphere (technical)	at	≡ 1 kgf/cm²	=
	bar	≡ Pa	≡ 10⁵ Pa
barye (CGS unit)		≡ 1 dyn/cm²	= 0.1 Pa
centimetre of mercury	cmHg	≡ × 1 cm ×	≈
centimetre of water (4 °C)	cmH₂O	≈ 999.972 kg/m³ × 1 cm ×	≈
foot of mercury (conventional)	ftHg	≡ × 1 ft ×	≈
foot of water (39.2 °F)	ftH₂O	≈ 999.972 kg/m³ × 1 ft ×	≈
inch of mercury (conventional)	inHg	≡ × 1 in ×	≈
inch of water (39.2 °F)	inH₂O	≈ 999.972 kg/m³ × 1 in ×	≈
kilogram-force per square millimetre	kgf/mm²	≡ 1 kgf/mm²	=
	ksi	≡ 1 kipf/sq in	≈
		≡ 1 long ton × / 1 sq ft	≈
micrometre of mercury	μmHg	≡ × 1 μm × ≈ 0.001 torr	≈
	mmHg	≡ × 1 mm × ≈ 1 torr	≈
millimetre of water (3.98 °C)	mmH₂O	≈ 999.972 kg/m³ × 1 mm × =	=
pascal (SI unit)	Pa	≡ N/m² = kg/(m⋅s²)	= 1 Pa^[31]
pièze (mts unit)	pz	≡	= = 1 kPa
	psf	≡ 1 lbf/ft²	≈
	psi	≡ 1 lbf/in²	≈
	pdl/sq ft	≡ 1 pdl/sq ft	≈
		≡ 1 short ton × / 1 sq ft	≈
	torr	≡ Pa	≈

Torque or moment of force

Torque!Name of unit!Symbol!Definition!Relation to SI units
pound-force-foot	lbf⋅ft	≡ × 1 lb × 1 ft	=
poundal-ft	pdl⋅ft	≡ 1 lb⋅ft²/s²	=
	lbf⋅in	≡ × 1 lb × 1 in	=
	kgf⋅m	≡ × N × m	=
newton-metre (SI unit)	N⋅m	≡ N × m = kg⋅m²/s²	=

Energy

Definition!Relation to SI units
	boe	≈	≈
British thermal unit (ISO)	BTU_ISO	≡	=
British thermal unit (International Table)	BTU_IT		=
British thermal unit (mean)	BTU_mean		≈
British thermal unit (thermochemical)	BTU_th		≈
British thermal unit (39 °F)	BTU_39 °F		≈
British thermal unit (59 °F)	BTU_59 °F	≡	=
British thermal unit (60 °F)	BTU_60 °F		≈
British thermal unit (63 °F)	BTU_63 °F		≈
calorie (International Table)	cal_IT	≡	=
calorie (mean)	cal_mean	of the energy required to warm one gram of air-free water from 0 °C to 100 °C at a pressure of 1 atm	≈
calorie (thermochemical)	cal_th	≡ 4.184 J	=
Calorie (US; FDA)	Cal	≡ 1 kcal =	=
calorie (3.98 °C)	cal_3.98 °C		≈
calorie (15 °C)	cal_15 °C	≡ 4.1855 J	=
calorie (20 °C)	cal_20 °C		≈
Celsius heat unit (International Table)	CHU_IT	≡ 1 BTU_IT × 1 K/°R	=
cubic centimetre of atmosphere; standard cubic centimetre	cc atm; scc	≡ 1 atm × 1 cm³	=
cubic foot of atmosphere; standard cubic foot	cu ft atm; scf	≡ 1 atm × 1 ft³	=
cubic foot of natural gas		≡	=
cubic yard of atmosphere; standard cubic yard	cu yd atm; scy	≡ 1 atm × 1 yd³	=
	eV	≡ e × 1 V	≡
erg (CGS unit)	erg	≡ 1 g⋅cm²/s²	= 10⁻⁷ J
	ft lbf	≡ × 1 lb × 1 ft	=
foot-poundal	ft pdl	≡ 1 lb⋅ft²/s²	=
gallon-atmosphere (imperial)	imp gal atm	≡ 1 atm × 1 gal (imp)	=
gallon-atmosphere (US)	US gal atm	≡ 1 atm × 1 gal (US)	=
	E_h	≡ m_e⋅α²⋅c² (= 2 Ry)	≈
	hp⋅h	≡ 1 hp × 1 h	=
	in lbf	≡ × 1 lb × 1 in	=
joule (SI unit)	J	The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force.	= 1 J = 1 m⋅N = 1 kg⋅m²/s² = 1 C⋅V = 1 W⋅s
	kcal; Cal	≡	=
kilowatt-hour Board of Trade Unit	kW⋅h; B.O.T.U.	≡ 1 kW × 1 h	=
	l atm; sl	≡ 1 atm × 1 L	=
		≡ 10¹⁵ BTU_IT	=
	Ry	≡ R_∞⋅ℎ⋅c	≈
therm (E.C.)		≡	=
therm (US)		≡	=
thermie	th	≡ 1 Mcal_IT	=
	TCE	≡ 7 Gcal_th	=
	toe	≡ 10 Gcal_IT	=
	tTNT	≡ 1 Gcal_th	=
	W⋅h	≡ 1 W × 1 h	=
	W⋅s	≡ 1 J	=

Power or heat flow rate

Definition!Relation to SI units
	atm ccm	≡ 1 atm × 1 cm³/min	=
	atm ccs	≡ 1 atm × 1 cm³/s	=
	atm cfh	≡ 1 atm × 1 cu ft/h	=
atmosphere-cubic foot per minute	atm cfm	≡ 1 atm × 1 cu ft/min	=
atmosphere-cubic foot per second	atm cfs	≡ 1 atm × 1 cu ft/s	=
BTU (International Table) per hour	BTU_IT/h	≡ 1 BTU_IT/h	≈
BTU (International Table) per minute	BTU_IT/min	≡ 1 BTU_IT/min	≈
BTU (International Table) per second	BTU_IT/s	≡ 1 BTU_IT/s	=
calorie (International Table) per second	cal_IT/s	≡ 1 cal_IT/s	=
erg per second	erg/s	≡ 1 erg/s	=
foot-pound-force per hour	ft⋅lbf/h	≡ 1 ft lbf/h	≈
foot-pound-force per minute	ft⋅lbf/min	≡ 1 ft lbf/min	=
foot-pound-force per second	ft⋅lbf/s	≡ 1 ft lbf/s	=
horsepower (boiler)	hp	-->	≈ 34.5 lb/h × 970.3 BTU_IT/lb	≈
horsepower (European electrical)	hp	≡ 75 kp⋅m/s	=
horsepower (electrical)	hp	≡ 746 W	=
horsepower (mechanical)	hp	≡ 550 ft⋅lbf/s	=
horsepower (metric)	hp or PS	≡ 75 m⋅kgf/s	=
litre-atmosphere per minute	L·atm/min	≡ 1 atm × 1 L/min	=
litre-atmosphere per second	L·atm/s	≡ 1 atm × 1 L/s	=
lusec	lusec	≡ 1 L·μmHg/s	≈
	p	≡ 100 m⋅kgf/s	=
square foot equivalent direct radiation	sq ft EDR	≡ 240 BTU_IT/h	≈
ton of air conditioning		≡ of ice melted / 24 h	≈
ton of refrigeration (imperial)		≡ × ice_IT / 24 h: ice_IT = 144 °F × 2326 J/kg⋅°F	≈
ton of refrigeration (IT)		≡ × ice_IT / 24 h: ice_IT = 144 °F × 2326 J/kg⋅°F	≈
watt (SI unit)	W	The power which in one second of time gives rise to one joule of energy.	= = 1 J/s = 1 N⋅m/s = 1 kg⋅m²/s³

Action

Action!Name of unit!Symbol!Definition!Relation to SI units
	au	≡ ℏ ≡	≈ ^[32]

Dynamic viscosity

Dynamic viscosity!Name of unit!Symbol!Definition!Relation to SI units
pascal second (SI unit)	Pa⋅s	≡ N⋅s/m², kg/(m⋅s)	= 1 Pa⋅s
poise (CGS unit)	P	≡ 1 barye⋅s	= 0.1 Pa⋅s
pound per foot hour	lb/(ft⋅h)	≡ 1 lb/(ft⋅h)	≈
pound per foot second	lb/(ft⋅s)	≡ 1 lb/(ft⋅s)	≈
pound-force second per square foot	lbf⋅s/ft²	≡ 1 lbf⋅s/ft²	≈
pound-force second per square inch	lbf⋅s/in²	≡ 1 lbf⋅s/in²	≈

Kinematic viscosity

Kinematic viscosity!Name of unit!Symbol!Definition!Relation to SI units
square foot per second	ft²/s	≡ 1 ft²/s	=
square metre per second (SI unit)	m²/s	≡ 1 m²/s	= 1 m²/s
stokes (CGS unit)	St	≡ 1 cm²/s	= 10⁻⁴ m²/s

Electric current

Definition!Relation to SI units
ampere (SI base unit)	A	≡ one coulomb of charge going past a given point per second.	(SI base unit)
electromagnetic unit abampere (CGS unit)	abamp	≘ 10 A	= 10 A
esu per second; statampere (CGS unit)	esu/s	≘ (10 A⋅cm/s) / c	≈

Electric charge

Electric charge!Name of unit!Symbol!Definition!Relation to SI units
abcoulomb electromagnetic unit (CGS unit)	abC; emu	≘ 10 C	= 10 C
	au	≡ e	=
	C	≡ charge of exactly 1/ elementary charges^[33]	= 1 C = 1 A⋅s
	F	≡ 1 mol × N_A⋅e	≈
	mA⋅h	≡ 0.001 A × 1 h	= 3.6 C
statcoulomb franklin; electrostatic unit (CGS unit)	statC; Fr; esu	≘ (10 A⋅cm) / c	≈

Electric dipole

Electric dipole!Name of unit!Symbol!Definition!Relation to SI units
atomic unit of electric dipole moment	ea₀		≈
coulomb-meter	C⋅m		= 1 C⋅m
	D	≡ 10⁻¹⁰ esu⋅Å	≘ ^[34]

Electromotive force, electric potential difference

Voltage, electromotive force!Name of unit!Symbol!Definition!Relation to SI units
abvolt (CGS unit)	abV	≘ 10⁻⁸ V	= 10⁻⁸ V
statvolt (CGS unit)	statV	≘ c⋅(1 μJ/A⋅m)	=
volt (SI unit)	V	The difference in electric potential across two points along a conducting wire carrying one ampere of constant current when the power dissipated between the points equals one watt.	= 1 V = 1 W/A = 1 J/C

Electrical resistance

Electrical resistance!Name of unit!Symbol!Definition!Relation to SI units
ohm (SI unit)	Ω	The resistance between two points in a conductor when one volt of electric potential difference, applied to these points, produces one ampere of current in the conductor.	= 1 Ω = 1 V/A

Capacitance

Capacitor's ability to store charge!Name of unit!Symbol!Definition!Relation to SI units
farad (SI unit)	F	The capacitance between two parallel plates that results in one volt of potential difference when charged by one coulomb of electricity.	= 1 F = 1 C/V

Magnetic flux

Magnetic flux!Name of unit!Symbol!Definition!Relation to SI units
maxwell (CGS unit)	Mx	≘ 10⁻⁸ Wb	= 10⁻⁸ Wb
weber (SI unit)	Wb	Magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.	= 1 Wb = 1 V⋅s

Magnetic flux density

What physicists call magnetic field is called magnetic flux density by electrical engineers and magnetic induction by applied mathematicians and electrical engineers.!Name of unit!Symbol!Definition!Relation to SI units
gauss (CGS unit)	G	≡ Mx/cm² ≘ 10⁻⁴ T	= 10⁻⁴ T ^[35]
tesla (SI unit)	T	≡ Wb/m²	= 1 T = 1 Wb/m²

Inductance

Inductance!Name of unit!Symbol!Definition!Relation to SI units
henry (SI unit)	H	The inductance of a closed circuit that produces one volt of electromotive force when the current in the circuit varies at a uniform rate of one ampere per second.	= 1 H = 1 Wb/A

Temperature

Temperature!Name of unit!Symbol!Definition!Relation to SI units
	°C	[°C] ≡ [K] − 273.15	[K] ≡ [°C] + 273.15
	°De		[K] = 373.15 − [°De] ×
	°F	[°F] ≡ [°C] × + 32	[K] ≡ ([°F] + 459.67) ×
	°N		[K] = [°N] × + 273.15
	°R;	[°R] ≡ [K] ×	[K] ≡ [°R] × 5/9
	°Ré		[K] = [°Ré] × + 273.15
	°Rø		[K] = ([°Rø] − 7.5) × + 273.15
	GM	[°F] ≡ [GM] × 25 + 250	[K] ≡ [GM] × + 394.26
kelvin (SI base unit)	K	≡ change in the thermodynamic temperature that results in a change of thermal energy by 1.380 649 × 10⁻²³ J.^[36]	(SI base unit)

Information entropy

Information entropy!Name of unit!Symbol!Definition!Relation to SI units!Relation to bits
natural unit of information nit; nepit	nat
	Sh	≡ ln(2) × nat	≈	= 1 bit
hartley ban	Hart; ban	≡ ln(10) × nat	≈
	bit; b			= 1 bit
		≡ 4 bits		= 2² bit
	B	≡ 8 bits		= 2³ bit
kilobyte (decimal)	kB	≡		= bit
kibibyte (kilobyte)	KiB	≡		= 2¹³ bit = bit

Modern standards (such as ISO 80000) prefer the shannon to the bit as a unit for a quantity of information entropy, whereas the (discrete) storage space of digital devices is measured in bits. Thus, uncompressed redundant data occupy more than one bit of storage per shannon of information entropy. The multiples of a bit listed above are usually used with this meaning.

Luminous intensity

The candela is the preferred nomenclature for the SI unit.

Luminous intensity
Name of unit	Symbol	Definition	Relation to SI units
candela (SI base unit)	cd	The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.	(SI base unit)
candlepower (new)	cp	≡ cd The use of candlepower as a unit is discouraged due to its ambiguity.	= 1 cd
candlepower (old, pre-1948)	cp	Varies and is poorly reproducible. Approximately 0.981 cd.	≈ 0.981 cd

Luminance

Luminance
Name of unit	Symbol	Definition	Relation to SI units
candela per square foot	cd/ft²	≡ cd/ft²	≈
candela per square inch	cd/in²	≡ cd/in²	≈
candela per square metre (SI unit); nit (deprecated)	cd/m²	≡ cd/m²	= 1 cd/m²
footlambert	fL	≡ (1/π) cd/ft²	≈
lambert	L	≡ (10⁴/π) cd/m²	≈
stilb (CGS unit)	sb	≡ 10⁴ cd/m²	= 10⁴ cd/m²

Illuminance

Illuminance
Name of unit	Symbol	Definition	Relation to SI units
footcandle lumen per square foot	fc	≡ lm/ft²	=
lumen per square inch	lm/in²	≡ lm/in²	≈
lux (SI unit)	lx	≡ lm/m²	= 1 lx = 1 lm/m²
phot (CGS unit)	ph	≡ lm/cm²	= 10⁴ lx

Radiation

Radiation – source activity

Radioactivity
Name of unit	Symbol	Definition	Relation to SI units
becquerel (SI unit)	Bq	≡ Number of disintegrations per second	= 1 Bq = 1/s
	Ci	≡ ^[37]	=
rutherford (H)	Rd	≡ 1 MBq	= 10⁶ Bq

Although becquerel (Bq) and hertz (Hz) both ultimately refer to the same SI base unit (s⁻¹), Hz is used only for periodic phenomena (i.e. repetitions at regular intervals), and Bq is only used for stochastic processes (i.e. at random intervals) associated with radioactivity.

Radiation – exposure

The roentgen is not an SI unit and the NIST strongly discourages its continued use.

Radiation – absorbed dose

Radiation – absorbed dose
Name of unit	Symbol	Definition	Relation to SI units
gray (SI unit)	Gy	≡ 1 J/kg^[38]	= 1 Gy = 1 J/kg = 1 m²⋅s²
	rad	≡ 0.01 Gy	= 0.01 Gy

Radiation – equivalent dose

Radiation – equivalent dose
Name of unit	Symbol	Definition	Relation to SI units
	rem	≡ 0.01 Sv	= 0.01 Sv
sievert (SI unit)	Sv	≡ 1 J/kg	= 1 Sv = 1 J/kg = 1 m²⋅s²

Although the definitions for sievert (Sv) and gray (Gy) would seem to indicate that they measure the same quantities, this is not the case. The effect of receiving a certain dose of radiation (given as Gy) is variable and depends on many factors, thus a new unit was needed to denote the biological effectiveness of that dose on the body; this is known as the equivalent dose and is shown in Sv. The general relationship between absorbed dose and equivalent dose can be represented as

H = Q ⋅ Dwhere H is the equivalent dose, D is the absorbed dose, and Q is a dimensionless quality factor. Thus, for any quantity of D measured in Gy, the numerical value for H measured in Sv may be different.

Notes and References

jobs . The astronomical unit gets fixed : Nature News & Comment . Nature . 10.1038/nature.2012.11416 . Nature.com . September 14, 2012. 123424704 . August 31, 2013.
"NIST Reference on Constants, Units, and Uncertainty."(2010). National Institute of Standards and Technology. Retrieved October 17, 2014.
Web site: NIST - National Institute of Standards and Technology. NIST.
Lide, D. (Ed.). (1990). Handbook of Chemistry and Physics (71st ed). Boca Raton, FL: CRC Press. Section 1.
National Bureau of Standards. (June 30, 1959). Refinement of values for the yard and the pound. Federal Register, viewed September 20, 2006 at National Geodetic Survey web site.
Web site: International Astronomical Union - IAU. www.iau.org.
Klein, Herbert Arthur.(1988). The Science of Measurement: a Historical Survey. Mineola, NY: Dover Publications 0-4862-5839-4.
https://www.bipm.org/en/publications/si-brochure/table8 International System of Units,
Book: 2000asqu.book.....C. Cox. Arthur N.. 2000. Allen's Astrophysical Quantities. 4th. AIP Press / Springer. New York. 0387987460.
Book: 2008gady.book.....B. Binney. James. Tremaine. Scott. 2008. Galactic Dynamics. 2nd. 978-0-691-13026-2. Princeton University Press. Princeton, NJ.
P. Kenneth Seidelmann, Ed. (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. p. 716 and s.v. parsec in Glossary.
Whitelaw, Ian. (2007). A Measure of All Things: The Story of Man and Measurement. New York: Macmillan 0-312-37026-1. p. 152.
De Vinne, Theodore Low (1900). The practice of typography: a treatise on the processes of type-making, the point system, the names, sizes, styles and prices of plain printing types 2nd ed. New York: The Century Co. p. 142 - 150.
Pasko, Wesley Washington (1894). American dictionary of printing and bookmaking. (1894). New York: Howard Lockwood. p. 521.
Thompson, A. and Taylor, B.N. (2008). Guide for the Use of the International System of Units (SI). National Institute of Standards and Technology Special Publication 811. p. 57.
Barry N. Taylor, Ed.,NIST Special Publication 330: The International System of Units (SI) (2001 Edition), Washington: US Government Printing Office, 43,"The 12th Conference Generale des Poids et Mesures (CGPM)...declares that the word "litre" may be employed as a special name for the cubic decimetre".
http://physics.nist.gov/cgi-bin/cuu/Value?ttme|search_for=atomic+unit+of+mass CODATA Value: atomic unit of mass.
The Swiss Federal Office for Metrology gives Zentner on a German language web page Web site: Metas: Masseinheiten - SI-Einheiten . 2006-10-09 . dead . https://web.archive.org/web/20060928011837/http://www.metas.ch/de/scales/systemch.html . 2006-09-28 . and quintal on the English translation of that page Web site: OFMET: Units of measure - SI units . 2006-10-09 . dead . https://web.archive.org/web/20010309033010/http://www.metas.ch/en/scales/systemch.html . 2001-03-09 . ; the unit is marked "spécifiquement suisse !"
see Callippic cycle for explanation of the differences
This is based on the average Gregorian year. See above for definition of year lengths.
Where UTC is observed, the length of this unit may increase or decrease
depending on the number of leap seconds which occur during the time interval in question.
The length of ancient lustral cycles was not constant; see Lustrum for more details
Pedersen O. (1983). "Glossary" in Coyne, G., Hoskin, M., and Pedersen, O. Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its 400th Anniversary. Vatican Observatory. Available from Astrophysics Data System.
Web site: CODATA Value: Planck time. physics.nist.gov. 2018-06-20.
Richards, E. G. (2013). "Calendars" in S. E. Urban & P. K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac. Mill Valley, CA: University Science Books.
The technical definition of tropical year is the period of time for the ecliptic longitude of the Sun to increase 360 degrees. (Urban & Seidelmann 2013, Glossary, s.v. year, tropical)
Richards, E. G. (2013). "Calendars" in S. E. Urban & P. K. Seidelmann, eds. Explanatory Supplement to the Astronomical Almanac. Mill Valley, CA: University Science Books. p. 587.
Until 1970 the UK Admiralty (and until 1954 the US) used other definitions of the nautical mile and hence the knot. See also
1. Length
http://physics.nist.gov/cuu/Constants/ CODATA Value: atomic unit of force
Barry N. Taylor, (April 1995), Guide for the Use of the International System of Units (SI) (NIST Special Publication 811), Washington, DC: US Government Printing Office, pp. 57 - 68.
Barry N. Taylor, (April 1995), Guide for the Use of the International System of Units (SI) (NIST Special Publication 811), Washington, DC: US Government Printing Office, p. 5.
http://www.bipm.org/en/si/si_brochure/chapter4/table7.html International System of Units,
Web site: SI brochure (2019). BIPM. 132. SI Brochure. May 23, 2019.
Robert G. Mortimer Physical chemistry, Academic Press, 2000, page 677
Standard for the Use of the International System of Units (SI): The Modern Metric System IEEE/ASTM SI 10-1997. (1997). New York and West Conshohocken, PA: Institute of Electrical and Electronics Engineers and American Society for Testing and Materials. Tables A.1 through A.5.
Web site: Mise en pratique. BIPM.
Ambler Thompson & Barry N. Taylor. (2008). Guide for the Use of the International System of Units (SI). Special Publication 811. Gaithersburg, MD: National Institute of Standards and Technology. p. 10.
Ambler Thompson & Barry N. Taylor. (2008). Guide for the Use of the International System of Units (SI). Special Publication 811. Gaithersburg, MD: National Institute of Standards and Technology. p. 5.