Units and Conversion Factors

SI Unit (Abbreviation)	Typical symbol	quantity
Mechanical
meter, m	x,y,z,l,d	Length
kilogram, kg	m	Mass
second, s	t	Time
meter/second, m/s	v, u	Velocity
newton, n	f	Force
newton-meter, nm	t	Torque
pascal, pa	p	Pressure
joule, j	w	Energy
watt, w	p,p	Power
radian, rad	α,β,γ,θ	Angle
radian/second, rad/s	ω	Angular velocity
Kg-m2	J	Mass polar moment of inertia
Electrical
coulomb, C	q, Q	Charge
ampere, A	i,I	(Electric) current
volt, V	v,V,e,E	Voltage
hertz, Hz	f	Frequency
radian per second, rad/s	ω	Radian frequency
voltampere, VA	S	Apparent power
watt, W	P	Average power
voltampere-reactive, var	Q	Reactive power
ohm, Ω	R	Resistance
henry, H	L	Inductance
farad, F	C	Capacitance
ohm, Ω	Z , X	Impedance, reactance
siemens, S	G	Conductance
siemens, S	Y, B	Admittance, susceptance
Thermal
kelvin, K	,θT	Temperature
watt, W	P, Q	Thermal power
joule, J	W	Heat energy
joule/kelvin, J/K	C	Thermal capacitance
watt/kelvin, W/K	G	Thermal capacitance
joule/(kelvin-kilogram), J/(K-kg)	cp	Specific heat
Magnetic
weber, Wb	φ	Flux
tesla, T	B	Flux density
ampere/meter, A/m	H	Magnetic field intensity
1/henry, H-1	ℜ	Reluctance
henry, H	℘	Permeance
ampere-turns, A	ℑ	Magnetomotive force

SI Prefixes
10-24	y	yocto	1024	Y	yotta
10-21	z	zepto	1021	Z	zetta
10-18	a	atto	1018	E	exa
10-15	f	femto	1015	P	peta
10-12	p	pico	1012	T	tera
10-9	n	nano	109	G	giga
10-6	μ	micro	106	M	mega
10-3	m	milli	103	k	kilo
10-2	c	centi	102	h	hecto
10-1	d	deci	101	da	Deca  or deka
Example usage: I= 118 A = 0.118 kA = 118000 mA.

Selected Constants

Permeability of free space = 0.4 π μH/m
Permittivity of free space = 8.8542 pf/m
Absolute zero (temperature) = 0 K = −273.2°C = −459.7°F = 0°R
Freezing point of water = 273.2 K = 0°C = 32°F = 491.7°R
g = acceleration of gravity = 9.807 m/s² = 32.17 ft/s²
G = gravitational constant = 66.72 pN (m²) (kg^-2)
c = speed of light in vacuum = 0.2998 m/ns = 299.8 km/s
Avogadro’s constant = 1.602 × 10²³ = molecules per mole
e = charge on electron = 0.1602 aC
m0 = electron rest mass = 9.11 × 10^-28 gram
1 revolution = 2π radians = 360 degrees
1 standard atmosphere (atm) = 760 mm Hg = 101.3 kPa = 29.92 in Hg =
14.696 psi
Air density = 1.225 kg/m³@ 1 atmosphere, 15°C, 1 u = 1 amu = 1 atomic
mass unit = 1.661 × 10^-27 kg
1 toe (1 tonne oil equivalent) = 41.868 GJ = 1270 m³ natural gas (STP) = 2.3 tonnes coal   

1 ton TNT = 4.184 GJ

Selected Conversion Factors

1 inch = 2.54 cm; 1 foot = 12 inches; 1 meter = 3.28084 feet
1 pound force (lbf)= 4.4482 newtons; 1 kilogram = 2.188 pound mass (lbm)
J in kg-m² = 0.0.04246 × J in lbm-ft²
1 atomic mass unit = u = 1.661 × 10^-27 kg
Electron/positron mass = 0.000549 u
Proton mass = 1.007276 u
Neutron mass = 1.008665 u
1 slug = 14.59 kilogram
1 foot-pound = 1.356 newton-meter
1 horsepower = 746 watts
1 British Thermal Unit (BTU) = 1055 joule
1 calorie = 4.19 joule
Temperature in Kelvin (K) = T_K
Temperature in degrees Celsius (°C) = T_C = T_K – 273.2
Temperature in degrees Fahrenheit (°F) = T_F = 1.8T_C + 32
Temperature in degrees Rankine (°R) = T_R = T_F + 459.7
1 milligauss = 1 mG = 0.1 microtesla = 0.1 μT
1 ton (refrigeration) = 3517 watts = 12 kBTU/hr
1 tonne = 1 metric ton = 1000 kg
Speed in rad/s = (2π/60) × speed in rpm (rpm = revolutions per minute)
1 day = 24 hours; 1 hour = 60 minutes; 1 minute = 60 seconds
1 nautical mile = 6000 ft = 1.1364 mile
1 knot = 1 nautical mile per hour = 1.1364 mph = 0.5080 m/s

Temperature Scales

Kelvin	Centigrade	Rankine	Fahrenheit
373 K	100°C	672°R	212°F
311 K	38°C	560°R	212°F
273 K	0°C	492°R	32°F
255 K	−18°C	460°R	0°F
0 K	−273°C	0°R	−460°F

Notes
One unit C = one unit K; one unit F = one unit R; one unit K = I.8 F units.
Absolute zero (0 K) = −459.67°F  = −273.15°C.
Normal human body temperature is 98.2°F (36.8°C).

Related posts:
Electrical unit