Important constants and conversion factors

Values for some physical constants and units

Constant	Value
Ångström (Å)	0.1 nm (exactly)
Standard atmosphere (that is, 1 atm)	101.325 kPa (exactly) =1.013 25 bar (exactly) = 760 torr (exactly) = 1.033 23 kg(force) cm-2 = 760 mmHg ; Standard pressure is now defined as 100 kPa exactly.
Atomic mass unit (u) = Dalton (Da)	12C/12 = 1.660 538 921 x 10-27 kg
Atomic unit of time = h/2πEh	2.418 884 326 502 x 10-17 s [934] (under revision)
Avogadro number (NA)	6.022 141 29 x 1023 mol-1 [934] (under revision)
Barn (b)	100 fm2 = 10-28 m2
Becquerel (Bq, unit of radioactivity)	One nuclear disintegration per second (1 Curie (Ci) = 3.7x1010 Bq, exactly)
Boltzmann constant (kB)	1.380 648 8 x 10-23 J K-1 [934] (under revision)
Bohr radius (a0, atomic unit of length)	0.529 177 2108 x 10-10 m [934] (under revision)
Curie (Ci)	3.7 x 1010 Bq (Bq = becquerel = s-1)
Celsius zero point (0 °C exactly)	273.15 K (exactly; a degree Celsius has the same size as one kelvin); Standard temperature is now defined as 273.15 K exactly.
Debye (D)	3.335 640 95 x 10-30 C m (= -0.208 194 35 e- Å)
Dyne (dyn) (force)	10-5 N
e (base for natural logarithms)	2.718 281 828 459 045 235 360 287 471 352 662 497 757 247 093 ...
Electromagnetic radiation	100 cm-1 = 109/nm = 1.197 KJ mol-1 ~ 3 THz
Electron volt (eV)	1.602 176 565 x 10-19 J (96.485 336 5 kJ mol-1; see also Faraday) [934]
Electron mass (me, atomic unit of mass)	9.109 382 91 x 10-31 kg [934] (under revision)
Elementary charge (e, atomic unit of charge)	(-) 1.602 176 565 x 10-19 C [934] (under revision)
Erg (erg) (energy)	10-7 J
Fahrenheit temperature scale (°F, obsolete)	(Fahrenheit temperature) = (Kelvin temperature) × 9⁄5 − 459.67 (Kelvin temperature) = (Fahrenheit temperature + 459.67) × 5⁄9
Faraday	96,485.3365 C mol-1 [934]
Gauss, G (magnetic flux density)	Mx cm-2 = 10-4 T ( Mx = maxwell; T = tesla)
The golden ratio (φ)	1.618 033 988 749 894 848 204 586 834 365 638 117 720 309 179 ...
Acceleration due to gravity (g, standard)	9.806 65 m s-2 (exactly)
Hartree (Eh, atomic unit of energy)	4.359 744 34 x 10-18 J [934] (under revision)
Kelvin (K)	The fraction 1/273.16 of the thermodynamic temperature of the triple point of water; (Absolute zero, 0 K = −273.15 °C or −459.67 °F).
Kilocalorie (kcal, thermochemical)	4.1840 kJ (exactly)
Liter, L	10-3m3 (exactly)
Loge(10)	2.302 585 092 994 045 684 017 991 454 684 364 207 601 101 488 ...
Relative/absolute mass of 12C	12 exactly / 1.992 646 705 x 10-26 kg
Maxwell, Mx (magnetic flux)	G cm2 = 10-8 Wb (G = gauss; Wb = weber)
Meter	see speed of light below
Molar concentration (M)	1 mol L-1 = 103 mol m-3
Molar gas constant (R =kBNA)	8.314 4621 J mol-1 K-1 [934] (= 0.082 057 46 L atm mol-1 K-1)
Molar volume of ideal gas (STP)	22.710 953 x 10-3 m3 mol-1
Nernst constant, = RT/F	25.692576 mV (25 °C)
Permeability of a vacuum (µ0) (Magnetic constant)	4π x 10-7 N A-2 (exactly) = 1.256 637 0614 µH m-1 (μN A-2) [934]
Permittivity of a vacuum (ε0) (Electric constant)	(μ0c2)-1 (exactly) = 8.854 187 817 pF m-1 [934]
Π (= circle circumference/diameter)	3.141 592 653 589 793 238 462 643 383 279 502 884 197 169 399 ...
Planck constant (h)	6.626 069 57 x 10-34 J s (under revision)
Reduced Planck constant (h/2π = atomic unit of action)	1.054 571 72 x 10-34 J s (under revision)
Poise, P (dynamic viscosity)	dyne s cm-2 = 0.1 Pa s
Radian	360°/2π = 57.295 779 513 082 3 °
Speed of light in vacuum, c0	299,792,458 m s-1 (exactly, also defines the meter) [934]
Standard temperature and pressure (STP)	100 kPa, 273.15 K (exactly)
Stokes, St (kinematic viscosity)	cm2 s-1= 10-4 m2 s-1
Terahertz (THz)	1012 s-1 (1 THz = 1 ps-1 33.355 640 952 cm-1 299.792 458 µm 0.004 135 669 2 eV 399.031 66 J mol-1)
Thermal energy (kT at 298 K)	2.478 kJ mol-1
Units	micro- µ 10-6; nano- n 10-9; pico- p 10-12; femto- f 10-15; atto- a 10-18 kilo- k 103; mega- M 106; giga- G 109; tera- T 1012; peta- P 1015
Wavelength (nm)	= 107/wavenumber (cm-1) (1 nm  3.33 564 095 attosecond)
Wavenumber (m-1)	= 109/wavelength (nm) (1 cm-1  0.029 979 2458 THz)
Year	= 365.242199 days = 31,556,925.9936 seconds

Note that the  SI unit definitions are under review for change soon; for example, the kelvin may be redefined in terms of an exactly defined value for the Boltzman constant and the kilogram may be defined in terms of its energy content [1031].

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This page was last updated by Martin Chaplin on 25 November, 2012