SciPy

Constants (scipy.constants)

Physical and mathematical constants and units.

Mathematical constants

pi Pi
golden Golden ratio
golden_ratio Golden ratio

Physical constants

c speed of light in vacuum
speed_of_light speed of light in vacuum
mu_0 the magnetic constant \(\mu_0\)
epsilon_0 the electric constant (vacuum permittivity), \(\epsilon_0\)
h the Planck constant \(h\)
Planck the Planck constant \(h\)
hbar \(\hbar = h/(2\pi)\)
G Newtonian constant of gravitation
gravitational_constant Newtonian constant of gravitation
g standard acceleration of gravity
e elementary charge
elementary_charge elementary charge
R molar gas constant
gas_constant molar gas constant
alpha fine-structure constant
fine_structure fine-structure constant
N_A Avogadro constant
Avogadro Avogadro constant
k Boltzmann constant
Boltzmann Boltzmann constant
sigma Stefan-Boltzmann constant \(\sigma\)
Stefan_Boltzmann Stefan-Boltzmann constant \(\sigma\)
Wien Wien displacement law constant
Rydberg Rydberg constant
m_e electron mass
electron_mass electron mass
m_p proton mass
proton_mass proton mass
m_n neutron mass
neutron_mass neutron mass

Constants database

In addition to the above variables, scipy.constants also contains the 2014 CODATA recommended values [CODATA2014] database containing more physical constants.

value(key) Value in physical_constants indexed by key
unit(key) Unit in physical_constants indexed by key
precision(key) Relative precision in physical_constants indexed by key
find([sub, disp]) Return list of physical_constant keys containing a given string.
ConstantWarning Accessing a constant no longer in current CODATA data set
scipy.constants.physical_constants

Dictionary of physical constants, of the format physical_constants[name] = (value, unit, uncertainty).

Available constants:

alpha particle mass 6.64465723e-27 kg
alpha particle mass energy equivalent 5.971920097e-10 J
alpha particle mass energy equivalent in MeV 3727.379378 MeV
alpha particle mass in u 4.00150617913 u
alpha particle molar mass 0.00400150617913 kg mol^-1
alpha particle-electron mass ratio 7294.29954136
alpha particle-proton mass ratio 3.97259968907
Angstrom star 1.00001495e-10 m
atomic mass constant 1.66053904e-27 kg
atomic mass constant energy equivalent 1.492418062e-10 J
atomic mass constant energy equivalent in MeV 931.4940954 MeV
atomic mass unit-electron volt relationship 931494095.4 eV
atomic mass unit-hartree relationship 34231776.902 E_h
atomic mass unit-hertz relationship 2.2523427206e+23 Hz
atomic mass unit-inverse meter relationship 7.5130066166e+14 m^-1
atomic mass unit-joule relationship 1.492418062e-10 J
atomic mass unit-kelvin relationship 1.08095438e+13 K
atomic mass unit-kilogram relationship 1.66053904e-27 kg
atomic unit of 1st hyperpolarizability 3.206361329e-53 C^3 m^3 J^-2
atomic unit of 2nd hyperpolarizability 6.235380085e-65 C^4 m^4 J^-3
atomic unit of action 1.0545718e-34 J s
atomic unit of charge 1.6021766208e-19 C
atomic unit of charge density 1.081202377e+12 C m^-3
atomic unit of current 0.006623618183 A
atomic unit of electric dipole mom. 8.478353552e-30 C m
atomic unit of electric field 5.142206707e+11 V m^-1
atomic unit of electric field gradient 9.717362356e+21 V m^-2
atomic unit of electric polarizability 1.6487772731e-41 C^2 m^2 J^-1
atomic unit of electric potential 27.21138602 V
atomic unit of electric quadrupole mom. 4.486551484e-40 C m^2
atomic unit of energy 4.35974465e-18 J
atomic unit of force 8.23872336e-08 N
atomic unit of length 5.2917721067e-11 m
atomic unit of mag. dipole mom. 1.854801999e-23 J T^-1
atomic unit of mag. flux density 235051.755 T
atomic unit of magnetizability 7.8910365886e-29 J T^-2
atomic unit of mass 9.10938356e-31 kg
atomic unit of mom.um 1.992851882e-24 kg m s^-1
atomic unit of permittivity 1.11265005605e-10 F m^-1
atomic unit of time 2.41888432651e-17 s
atomic unit of velocity 2187691.26277 m s^-1
Avogadro constant 6.022140857e+23 mol^-1
Bohr magneton 9.274009994e-24 J T^-1
Bohr magneton in eV/T 5.7883818012e-05 eV T^-1
Bohr magneton in Hz/T 13996245042.0 Hz T^-1
Bohr magneton in inverse meters per tesla 46.68644814 m^-1 T^-1
Bohr magneton in K/T 0.67171405 K T^-1
Bohr radius 5.2917721067e-11 m
Boltzmann constant 1.38064852e-23 J K^-1
Boltzmann constant in eV/K 8.6173303e-05 eV K^-1
Boltzmann constant in Hz/K 20836612000.0 Hz K^-1
Boltzmann constant in inverse meters per kelvin 69.503457 m^-1 K^-1
characteristic impedance of vacuum 376.730313462 ohm
classical electron radius 2.8179403227e-15 m
Compton wavelength 2.4263102367e-12 m
Compton wavelength over 2 pi 3.8615926764e-13 m
conductance quantum 7.748091731e-05 S
conventional value of Josephson constant 4.835979e+14 Hz V^-1
conventional value of von Klitzing constant 25812.807 ohm
Cu x unit 1.00207697e-13 m
deuteron g factor 0.8574382311
deuteron mag. mom. 4.33073504e-27 J T^-1
deuteron mag. mom. to Bohr magneton ratio 0.0004669754554
deuteron mag. mom. to nuclear magneton ratio 0.8574382311
deuteron mass 3.343583719e-27 kg
deuteron mass energy equivalent 3.005063183e-10 J
deuteron mass energy equivalent in MeV 1875.612928 MeV
deuteron mass in u 2.01355321275 u
deuteron molar mass 0.00201355321274 kg mol^-1
deuteron rms charge radius 2.1413e-15 m
deuteron-electron mag. mom. ratio -0.0004664345535
deuteron-electron mass ratio 3670.48296785
deuteron-neutron mag. mom. ratio -0.44820652
deuteron-proton mag. mom. ratio 0.3070122077
deuteron-proton mass ratio 1.99900750087
electric constant 8.85418781762e-12 F m^-1
electron charge to mass quotient -1.758820024e+11 C kg^-1
electron g factor -2.00231930436
electron gyromag. ratio 1.760859644e+11 s^-1 T^-1
electron gyromag. ratio over 2 pi 28024.95164 MHz T^-1
electron mag. mom. -9.28476462e-24 J T^-1
electron mag. mom. anomaly 0.00115965218091
electron mag. mom. to Bohr magneton ratio -1.00115965218
electron mag. mom. to nuclear magneton ratio -1838.28197234
electron mass 9.10938356e-31 kg
electron mass energy equivalent 8.18710565e-14 J
electron mass energy equivalent in MeV 0.5109989461 MeV
electron mass in u 0.00054857990907 u
electron molar mass 5.4857990907e-07 kg mol^-1
electron to alpha particle mass ratio 0.00013709335548
electron to shielded helion mag. mom. ratio 864.058257
electron to shielded proton mag. mom. ratio -658.2275971
electron volt 1.6021766208e-19 J
electron volt-atomic mass unit relationship 1.0735441105e-09 u
electron volt-hartree relationship 0.03674932248 E_h
electron volt-hertz relationship 2.417989262e+14 Hz
electron volt-inverse meter relationship 806554.4005 m^-1
electron volt-joule relationship 1.6021766208e-19 J
electron volt-kelvin relationship 11604.5221 K
electron volt-kilogram relationship 1.782661907e-36 kg
electron-deuteron mag. mom. ratio -2143.923499
electron-deuteron mass ratio 0.000272443710748
electron-helion mass ratio 0.000181954307485
electron-muon mag. mom. ratio 206.766988
electron-muon mass ratio 0.0048363317
electron-neutron mag. mom. ratio 960.9205
electron-neutron mass ratio 0.00054386734428
electron-proton mag. mom. ratio -658.2106866
electron-proton mass ratio 0.000544617021352
electron-tau mass ratio 0.000287592
electron-triton mass ratio 0.00018192000622
elementary charge 1.6021766208e-19 C
elementary charge over h 2.417989262e+14 A J^-1
Faraday constant 96485.33289 C mol^-1
Faraday constant for conventional electric current 96485.3251 C_90 mol^-1
Fermi coupling constant 1.1663787e-05 GeV^-2
fine-structure constant 0.0072973525664
first radiation constant 3.74177179e-16 W m^2
first radiation constant for spectral radiance 1.191042953e-16 W m^2 sr^-1
Hartree energy 4.35974465e-18 J
Hartree energy in eV 27.21138602 eV
hartree-atomic mass unit relationship 2.9212623197e-08 u
hartree-electron volt relationship 27.21138602 eV
hartree-hertz relationship 6.57968392071e+15 Hz
hartree-inverse meter relationship 21947463.137 m^-1
hartree-joule relationship 4.35974465e-18 J
hartree-kelvin relationship 315775.13 K
hartree-kilogram relationship 4.850870129e-35 kg
helion g factor -4.255250616
helion mag. mom. -1.074617522e-26 J T^-1
helion mag. mom. to Bohr magneton ratio -0.001158740958
helion mag. mom. to nuclear magneton ratio -2.127625308
helion mass 5.0064127e-27 kg
helion mass energy equivalent 4.499539341e-10 J
helion mass energy equivalent in MeV 2808.391586 MeV
helion mass in u 3.01493224673 u
helion molar mass 0.00301493224673 kg mol^-1
helion-electron mass ratio 5495.88527922
helion-proton mass ratio 2.99315267046
hertz-atomic mass unit relationship 4.4398216616e-24 u
hertz-electron volt relationship 4.135667662e-15 eV
hertz-hartree relationship 1.51982984601e-16 E_h
hertz-inverse meter relationship 3.33564095198e-09 m^-1
hertz-joule relationship 6.62607004e-34 J
hertz-kelvin relationship 4.7992447e-11 K
hertz-kilogram relationship 7.372497201e-51 kg
inverse fine-structure constant 137.035999139
inverse meter-atomic mass unit relationship 1.331025049e-15 u
inverse meter-electron volt relationship 1.2398419739e-06 eV
inverse meter-hartree relationship 4.55633525277e-08 E_h
inverse meter-hertz relationship 299792458.0 Hz
inverse meter-joule relationship 1.986445824e-25 J
inverse meter-kelvin relationship 0.0143877736 K
inverse meter-kilogram relationship 2.210219057e-42 kg
inverse of conductance quantum 12906.4037278 ohm
Josephson constant 4.835978525e+14 Hz V^-1
joule-atomic mass unit relationship 6700535363.0 u
joule-electron volt relationship 6.241509126e+18 eV
joule-hartree relationship 2.293712317e+17 E_h
joule-hertz relationship 1.509190205e+33 Hz
joule-inverse meter relationship 5.034116651e+24 m^-1
joule-kelvin relationship 7.2429731e+22 K
joule-kilogram relationship 1.11265005605e-17 kg
kelvin-atomic mass unit relationship 9.2510842e-14 u
kelvin-electron volt relationship 8.6173303e-05 eV
kelvin-hartree relationship 3.1668105e-06 E_h
kelvin-hertz relationship 20836612000.0 Hz
kelvin-inverse meter relationship 69.503457 m^-1
kelvin-joule relationship 1.38064852e-23 J
kelvin-kilogram relationship 1.53617865e-40 kg
kilogram-atomic mass unit relationship 6.022140857e+26 u
kilogram-electron volt relationship 5.60958865e+35 eV
kilogram-hartree relationship 2.061485823e+34 E_h
kilogram-hertz relationship 1.356392512e+50 Hz
kilogram-inverse meter relationship 4.524438411e+41 m^-1
kilogram-joule relationship 8.98755178737e+16 J
kilogram-kelvin relationship 6.5096595e+39 K
lattice parameter of silicon 5.431020504e-10 m
Loschmidt constant (273.15 K, 100 kPa) 2.6516467e+25 m^-3
Loschmidt constant (273.15 K, 101.325 kPa) 2.6867811e+25 m^-3
mag. constant 1.25663706144e-06 N A^-2
mag. flux quantum 2.067833831e-15 Wb
Mo x unit 1.00209952e-13 m
molar gas constant 8.3144598 J mol^-1 K^-1
molar mass constant 0.001 kg mol^-1
molar mass of carbon-12 0.012 kg mol^-1
molar Planck constant 3.990312711e-10 J s mol^-1
molar Planck constant times c 0.119626565582 J m mol^-1
molar volume of ideal gas (273.15 K, 100 kPa) 0.022710947 m^3 mol^-1
molar volume of ideal gas (273.15 K, 101.325 kPa) 0.022413962 m^3 mol^-1
molar volume of silicon 1.205883214e-05 m^3 mol^-1
muon Compton wavelength 1.173444111e-14 m
muon Compton wavelength over 2 pi 1.867594308e-15 m
muon g factor -2.0023318418
muon mag. mom. -4.49044826e-26 J T^-1
muon mag. mom. anomaly 0.00116592089
muon mag. mom. to Bohr magneton ratio -0.00484197048
muon mag. mom. to nuclear magneton ratio -8.89059705
muon mass 1.883531594e-28 kg
muon mass energy equivalent 1.692833774e-11 J
muon mass energy equivalent in MeV 105.6583745 MeV
muon mass in u 0.1134289257 u
muon molar mass 0.0001134289257 kg mol^-1
muon-electron mass ratio 206.7682826
muon-neutron mass ratio 0.1124545167
muon-proton mag. mom. ratio -3.183345142
muon-proton mass ratio 0.1126095262
muon-tau mass ratio 0.0594649
natural unit of action 1.0545718e-34 J s
natural unit of action in eV s 6.582119514e-16 eV s
natural unit of energy 8.18710565e-14 J
natural unit of energy in MeV 0.5109989461 MeV
natural unit of length 3.8615926764e-13 m
natural unit of mass 9.10938356e-31 kg
natural unit of mom.um 2.730924488e-22 kg m s^-1
natural unit of mom.um in MeV/c 0.5109989461 MeV/c
natural unit of time 1.28808866712e-21 s
natural unit of velocity 299792458.0 m s^-1
neutron Compton wavelength 1.31959090481e-15 m
neutron Compton wavelength over 2 pi 2.1001941536e-16 m
neutron g factor -3.82608545
neutron gyromag. ratio 183247172.0 s^-1 T^-1
neutron gyromag. ratio over 2 pi 29.1646933 MHz T^-1
neutron mag. mom. -9.662365e-27 J T^-1
neutron mag. mom. to Bohr magneton ratio -0.00104187563
neutron mag. mom. to nuclear magneton ratio -1.91304273
neutron mass 1.674927471e-27 kg
neutron mass energy equivalent 1.505349739e-10 J
neutron mass energy equivalent in MeV 939.5654133 MeV
neutron mass in u 1.00866491588 u
neutron molar mass 0.00100866491588 kg mol^-1
neutron to shielded proton mag. mom. ratio -0.68499694
neutron-electron mag. mom. ratio 0.00104066882
neutron-electron mass ratio 1838.68366158
neutron-muon mass ratio 8.89248408
neutron-proton mag. mom. ratio -0.68497934
neutron-proton mass difference 2.30557377e-30
neutron-proton mass difference energy equivalent 2.07214637e-13
neutron-proton mass difference energy equivalent in MeV 1.29333205
neutron-proton mass difference in u 0.001388449
neutron-proton mass ratio 1.00137841898
neutron-tau mass ratio 0.52879
Newtonian constant of gravitation 6.67408e-11 m^3 kg^-1 s^-2
Newtonian constant of gravitation over h-bar c 6.70861e-39 (GeV/c^2)^-2
nuclear magneton 5.050783699e-27 J T^-1
nuclear magneton in eV/T 3.152451255e-08 eV T^-1
nuclear magneton in inverse meters per tesla 0.02542623432 m^-1 T^-1
nuclear magneton in K/T 0.0003658269 K T^-1
nuclear magneton in MHz/T 7.622593285 MHz T^-1
Planck constant 6.62607004e-34 J s
Planck constant in eV s 4.135667662e-15 eV s
Planck constant over 2 pi 1.0545718e-34 J s
Planck constant over 2 pi in eV s 6.582119514e-16 eV s
Planck constant over 2 pi times c in MeV fm 197.3269788 MeV fm
Planck length 1.616229e-35 m
Planck mass 2.17647e-08 kg
Planck mass energy equivalent in GeV 1.22091e+19 GeV
Planck temperature 1.416808e+32 K
Planck time 5.39116e-44 s
proton charge to mass quotient 95788332.26 C kg^-1
proton Compton wavelength 1.32140985396e-15 m
proton Compton wavelength over 2 pi 2.10308910109e-16 m
proton g factor 5.585694702
proton gyromag. ratio 267522190.0 s^-1 T^-1
proton gyromag. ratio over 2 pi 42.57747892 MHz T^-1
proton mag. mom. 1.4106067873e-26 J T^-1
proton mag. mom. to Bohr magneton ratio 0.0015210322053
proton mag. mom. to nuclear magneton ratio 2.7928473508
proton mag. shielding correction 2.5691e-05
proton mass 1.672621898e-27 kg
proton mass energy equivalent 1.503277593e-10 J
proton mass energy equivalent in MeV 938.2720813 MeV
proton mass in u 1.00727646688 u
proton molar mass 0.00100727646688 kg mol^-1
proton rms charge radius 8.751e-16 m
proton-electron mass ratio 1836.15267389
proton-muon mass ratio 8.88024338
proton-neutron mag. mom. ratio -1.45989805
proton-neutron mass ratio 0.99862347844
proton-tau mass ratio 0.528063
quantum of circulation 0.00036369475486 m^2 s^-1
quantum of circulation times 2 0.00072738950972 m^2 s^-1
Rydberg constant 10973731.5685 m^-1
Rydberg constant times c in Hz 3.28984196036e+15 Hz
Rydberg constant times hc in eV 13.605693009 eV
Rydberg constant times hc in J 2.179872325e-18 J
Sackur-Tetrode constant (1 K, 100 kPa) -1.1517084
Sackur-Tetrode constant (1 K, 101.325 kPa) -1.1648714
second radiation constant 0.0143877736 m K
shielded helion gyromag. ratio 203789458.5 s^-1 T^-1
shielded helion gyromag. ratio over 2 pi 32.43409966 MHz T^-1
shielded helion mag. mom. -1.07455308e-26 J T^-1
shielded helion mag. mom. to Bohr magneton ratio -0.001158671471
shielded helion mag. mom. to nuclear magneton ratio -2.12749772
shielded helion to proton mag. mom. ratio -0.7617665603
shielded helion to shielded proton mag. mom. ratio -0.7617861313
shielded proton gyromag. ratio 267515317.1 s^-1 T^-1
shielded proton gyromag. ratio over 2 pi 42.57638507 MHz T^-1
shielded proton mag. mom. 1.410570547e-26 J T^-1
shielded proton mag. mom. to Bohr magneton ratio 0.001520993128
shielded proton mag. mom. to nuclear magneton ratio 2.7927756
speed of light in vacuum 299792458.0 m s^-1
standard acceleration of gravity 9.80665 m s^-2
standard atmosphere 101325.0 Pa
standard-state pressure 100000.0 Pa
Stefan-Boltzmann constant 5.670367e-08 W m^-2 K^-4
tau Compton wavelength 6.97787e-16 m
tau Compton wavelength over 2 pi 1.11056e-16 m
tau mass 3.16747e-27 kg
tau mass energy equivalent 2.84678e-10 J
tau mass energy equivalent in MeV 1776.82 MeV
tau mass in u 1.90749 u
tau molar mass 0.00190749 kg mol^-1
tau-electron mass ratio 3477.15
tau-muon mass ratio 16.8167
tau-neutron mass ratio 1.89111
tau-proton mass ratio 1.89372
Thomson cross section 6.6524587158e-29 m^2
triton g factor 5.95792492
triton mag. mom. 1.504609503e-26 J T^-1
triton mag. mom. to Bohr magneton ratio 0.0016223936616
triton mag. mom. to nuclear magneton ratio 2.97896246
triton mass 5.007356665e-27 kg
triton mass energy equivalent 4.500387735e-10 J
triton mass energy equivalent in MeV 2808.921112 MeV
triton mass in u 3.01550071632 u
triton molar mass 0.00301550071632 kg mol^-1
triton-electron mass ratio 5496.92153588
triton-proton mass ratio 2.99371703348
unified atomic mass unit 1.66053904e-27 kg
von Klitzing constant 25812.8074555 ohm
weak mixing angle 0.2223
Wien frequency displacement law constant 58789238000.0 Hz K^-1
Wien wavelength displacement law constant 0.0028977729 m K
{220} lattice spacing of silicon 1.920155714e-10 m

Units

SI prefixes

yotta \(10^{24}\)
zetta \(10^{21}\)
exa \(10^{18}\)
peta \(10^{15}\)
tera \(10^{12}\)
giga \(10^{9}\)
mega \(10^{6}\)
kilo \(10^{3}\)
hecto \(10^{2}\)
deka \(10^{1}\)
deci \(10^{-1}\)
centi \(10^{-2}\)
milli \(10^{-3}\)
micro \(10^{-6}\)
nano \(10^{-9}\)
pico \(10^{-12}\)
femto \(10^{-15}\)
atto \(10^{-18}\)
zepto \(10^{-21}\)

Binary prefixes

kibi \(2^{10}\)
mebi \(2^{20}\)
gibi \(2^{30}\)
tebi \(2^{40}\)
pebi \(2^{50}\)
exbi \(2^{60}\)
zebi \(2^{70}\)
yobi \(2^{80}\)

Mass

gram \(10^{-3}\) kg
metric_ton \(10^{3}\) kg
grain one grain in kg
lb one pound (avoirdupous) in kg
pound one pound (avoirdupous) in kg
blob one inch version of a slug in kg (added in 1.0.0)
slinch one inch version of a slug in kg (added in 1.0.0)
slug one slug in kg (added in 1.0.0)
oz one ounce in kg
ounce one ounce in kg
stone one stone in kg
grain one grain in kg
long_ton one long ton in kg
short_ton one short ton in kg
troy_ounce one Troy ounce in kg
troy_pound one Troy pound in kg
carat one carat in kg
m_u atomic mass constant (in kg)
u atomic mass constant (in kg)
atomic_mass atomic mass constant (in kg)

Angle

degree degree in radians
arcmin arc minute in radians
arcminute arc minute in radians
arcsec arc second in radians
arcsecond arc second in radians

Time

minute one minute in seconds
hour one hour in seconds
day one day in seconds
week one week in seconds
year one year (365 days) in seconds
Julian_year one Julian year (365.25 days) in seconds

Length

inch one inch in meters
foot one foot in meters
yard one yard in meters
mile one mile in meters
mil one mil in meters
pt one point in meters
point one point in meters
survey_foot one survey foot in meters
survey_mile one survey mile in meters
nautical_mile one nautical mile in meters
fermi one Fermi in meters
angstrom one Angstrom in meters
micron one micron in meters
au one astronomical unit in meters
astronomical_unit one astronomical unit in meters
light_year one light year in meters
parsec one parsec in meters

Pressure

atm standard atmosphere in pascals
atmosphere standard atmosphere in pascals
bar one bar in pascals
torr one torr (mmHg) in pascals
mmHg one torr (mmHg) in pascals
psi one psi in pascals

Area

hectare one hectare in square meters
acre one acre in square meters

Volume

liter one liter in cubic meters
litre one liter in cubic meters
gallon one gallon (US) in cubic meters
gallon_US one gallon (US) in cubic meters
gallon_imp one gallon (UK) in cubic meters
fluid_ounce one fluid ounce (US) in cubic meters
fluid_ounce_US one fluid ounce (US) in cubic meters
fluid_ounce_imp one fluid ounce (UK) in cubic meters
bbl one barrel in cubic meters
barrel one barrel in cubic meters

Speed

kmh kilometers per hour in meters per second
mph miles per hour in meters per second
mach one Mach (approx., at 15 C, 1 atm) in meters per second
speed_of_sound one Mach (approx., at 15 C, 1 atm) in meters per second
knot one knot in meters per second

Temperature

zero_Celsius zero of Celsius scale in Kelvin
degree_Fahrenheit one Fahrenheit (only differences) in Kelvins
convert_temperature(val, old_scale, new_scale) Convert from a temperature scale to another one among Celsius, Kelvin, Fahrenheit and Rankine scales.
C2K(*args, **kwds) C2K is deprecated!
K2C(*args, **kwds) K2C is deprecated!
F2C(*args, **kwds) F2C is deprecated!
C2F(*args, **kwds) C2F is deprecated!
F2K(*args, **kwds) F2K is deprecated!
K2F(*args, **kwds) K2F is deprecated!

Energy

eV one electron volt in Joules
electron_volt one electron volt in Joules
calorie one calorie (thermochemical) in Joules
calorie_th one calorie (thermochemical) in Joules
calorie_IT one calorie (International Steam Table calorie, 1956) in Joules
erg one erg in Joules
Btu one British thermal unit (International Steam Table) in Joules
Btu_IT one British thermal unit (International Steam Table) in Joules
Btu_th one British thermal unit (thermochemical) in Joules
ton_TNT one ton of TNT in Joules

Power

hp one horsepower in watts
horsepower one horsepower in watts

Force

dyn one dyne in newtons
dyne one dyne in newtons
lbf one pound force in newtons
pound_force one pound force in newtons
kgf one kilogram force in newtons
kilogram_force one kilogram force in newtons

Optics

lambda2nu(lambda_) Convert wavelength to optical frequency
nu2lambda(nu) Convert optical frequency to wavelength.

References

[CODATA2014]

CODATA Recommended Values of the Fundamental Physical Constants 2014.

http://physics.nist.gov/cuu/Constants/index.html