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# Constants (`scipy.constants`)

Physical and mathematical constants and units.

## Mathematical constants

`pi` | Pi
`golden` | Golden ratio
`golden_ratio` | Golden ratio

## Physical constants

The following physical constants are available as attributes of `scipy.constants`. All units are SI.

Attribute | Quantity | Units
--- | --- | ---
`c` | speed of light in vacuum | m s^-1
`speed_of_light` | speed of light in vacuum | m s^-1
`mu_0` | the magnetic constant \(\mu_0\) | N A^-2
`epsilon_0` | the electric constant (vacuum permittivity), \(\epsilon_0\) | F m^-1
`h` | the Planck constant \(h\) | J Hz^-1
`Planck` | the Planck constant \(h\) | J Hz^-1
`hbar` | the reduced Planck constant, \(\hbar = h/(2\pi)\) | J s
`G` | Newtonian constant of gravitation | m^3 kg^-1 s^-2
`gravitational_constant` | Newtonian constant of gravitation | m^3 kg^-1 s^-2
`g` | standard acceleration of gravity | m s^-2
`e` | elementary charge | C
`elementary_charge` | elementary charge | C
`R` | molar gas constant | J mol^-1 K^-1
`gas_constant` | molar gas constant | J mol^-1 K^-1
`alpha` | fine-structure constant | (unitless)
`fine_structure` | fine-structure constant | (unitless)
`N_A` | Avogadro constant | mol^-1
`Avogadro` | Avogadro constant | mol^-1
`k` | Boltzmann constant | J K^-1
`Boltzmann` | Boltzmann constant | J K^-1
`sigma` | Stefan-Boltzmann constant \(\sigma\) | W m^-2 K^-4
`Stefan_Boltzmann` | Stefan-Boltzmann constant \(\sigma\) | W m^-2 K^-4
`Wien` | Wien wavelength displacement law constant | m K
`Rydberg` | Rydberg constant | m^-1
`m_e` | electron mass | kg
`electron_mass` | electron mass | kg
`m_p` | proton mass | kg
`proton_mass` | proton mass | kg
`m_n` | neutron mass | kg
`neutron_mass` | neutron mass | kg

### Constants database

In addition to the above variables, `scipy.constants` also contains the 2022 CODATA recommended values [CODATA2022] 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)`. The CODATA database uses ellipses to indicate that a value is defined (exactly) in terms of others but cannot be represented exactly with the allocated number of digits. In these cases, SciPy calculates the derived value and reports it to the full precision of a Python `float`. Although `physical_constants` lists the uncertainty as `0.0` to indicate that the CODATA value is exact, the value in `physical_constants` is still subject to the truncation error inherent in double-precision representation.

Available constants:

`alpha particle mass` | 6.644657345e-27 kg
`alpha particle mass energy equivalent` | 5.9719201997e-10 J
`alpha particle mass energy equivalent in MeV` | 3727.3794118 MeV
`alpha particle mass in u` | 4.001506179129 u
`alpha particle molar mass` | 0.0040015061833 kg mol^-1
`alpha particle relative atomic mass` | 4.001506179129
`alpha particle rms charge radius` | 1.6785e-15 m
`alpha particle-electron mass ratio` | 7294.29954171
`alpha particle-proton mass ratio` | 3.972599690252
`Angstrom star` | 1.00001495e-10 m
`atomic mass constant` | 1.66053906892e-27 kg
`atomic mass constant energy equivalent` | 1.49241808768e-10 J
`atomic mass constant energy equivalent in MeV` | 931.49410372 MeV
`atomic mass unit-electron volt relationship` | 931494103.72 eV
`atomic mass unit-hartree relationship` | 34231776.922 E_h
`atomic mass unit-hertz relationship` | 2.25234272185e+23 Hz
`atomic mass unit-inverse meter relationship` | 751300662090000.0 m^-1
`atomic mass unit-joule relationship` | 1.49241808768e-10 J
`atomic mass unit-kelvin relationship` | 10809540206700.0 K
`atomic mass unit-kilogram relationship` | 1.66053906892e-27 kg
`atomic unit of 1st hyperpolarizability` | 3.2063612996e-53 C^3 m^3 J^-2
`atomic unit of 2nd hyperpolarizability` | 6.2353799735e-65 C^4 m^4 J^-3
`atomic unit of action` | 1.0545718176461565e-34 J s
`atomic unit of charge` | 1.602176634e-19 C
`atomic unit of charge density` | 1081202386770.0 C m^-3
`atomic unit of current` | 0.0066236182375082 A
`atomic unit of electric dipole mom.` | 8.4783536198e-30 C m
`atomic unit of electric field` | 514220675112.0 V m^-1
`atomic unit of electric field gradient` | 9.7173624424e+21 V m^-2
`atomic unit of electric polarizability` | 1.64877727212e-41 C^2 m^2 J^-1
`atomic unit of electric potential` | 27.211386245981 V
`atomic unit of electric quadrupole mom.` | 4.4865515185e-40 C m^2
`atomic unit of energy` | 4.359744722206e-18 J
`atomic unit of force` | 8.2387235038e-08 N
`atomic unit of length` | 5.29177210544e-11 m
`atomic unit of mag. dipole mom.` | 1.85480201315e-23 J T^-1
`atomic unit of mag. flux density` | 235051.757077 T
`atomic unit of magnetizability` | 7.8910365794e-29 J T^-2
`atomic unit of mass` | 9.1093837139e-31 kg
`atomic unit of momentum` | 1.99285191545e-24 kg m s^-1
`atomic unit of permittivity` | 1.1126500562e-10 F m^-1
`atomic unit of time` | 2.4188843265864e-17 s
`atomic unit of velocity` | 2187691.26216 m s^-1
`Avogadro constant` | 6.02214076e+23 mol^-1
`Bohr magneton` | 9.2740100657e-24 J T^-1
`Bohr magneton in eV/T` | 5.7883817982e-05 eV T^-1
`Bohr magneton in Hz/T` | 13996244917.1 Hz T^-1
`Bohr magneton in inverse meter per tesla` | 46.686447719 m^-1 T^-1
`Bohr magneton in K/T` | 0.67171381472 K T^-1
`Bohr radius` | 5.29177210544e-11 m
`Boltzmann constant` | 1.380649e-23 J K^-1
`Boltzmann constant in eV/K` | 8.617333262145179e-05 eV K^-1
`Boltzmann constant in Hz/K` | 20836619123.327576 Hz K^-1
`Boltzmann constant in inverse meter per kelvin` | 69.50348004861274 m^-1 K^-1
`characteristic impedance of vacuum` | 376.730313412 ohm
`classical electron radius` | 2.8179403205e-15 m
`Compton wavelength` | 2.42631023538e-12 m
`conductance quantum` | 7.748091729863649e-05 S
`conventional value of ampere-90` | 1.0000000888714378 A
`conventional value of coulomb-90` | 1.0000000888714378 C
`conventional value of farad-90` | 0.9999999822063325 F
`conventional value of henry-90` | 1.0000000177936679 H
`conventional value of Josephson constant` | 483597900000000.0 Hz V^-1
`conventional value of ohm-90` | 1.0000000177936679 ohm
`conventional value of volt-90` | 1.0000001066651072 V
`conventional value of von Klitzing constant` | 25812.807 ohm
`conventional value of watt-90` | 1.0000001955365543 W
`Copper x unit` | 1.00207697e-13 m
`deuteron g factor` | 0.8574382335
`deuteron mag. mom.` | 4.330735087e-27 J T^-1
`deuteron mag. mom. to Bohr magneton ratio` | 0.0004669754568
`deuteron mag. mom. to nuclear magneton ratio` | 0.8574382335
`deuteron mass` | 3.3435837768e-27 kg
`deuteron mass energy equivalent` | 3.00506323491e-10 J
`deuteron mass energy equivalent in MeV` | 1875.612945 MeV
`deuteron mass in u` | 2.013553212544 u
`deuteron molar mass` | 0.00201355321466 kg mol^-1
`deuteron relative atomic mass` | 2.013553212544
`deuteron rms charge radius` | 2.12778e-15 m
`deuteron-electron mag. mom. ratio` | -0.000466434555
`deuteron-electron mass ratio` | 3670.482967655
`deuteron-neutron mag. mom. ratio` | -0.44820652
`deuteron-proton mag. mom. ratio` | 0.3070122093
`deuteron-proton mass ratio` | 1.9990075012699
`electron charge to mass quotient` | -175882000838.0 C kg^-1
`electron g factor` | -2.00231930436092
`electron gyromag. ratio` | 176085962784.0 s^-1 T^-1
`electron gyromag. ratio in MHz/T` | 28024.9513861 MHz T^-1
`electron mag. mom.` | -9.2847646917e-24 J T^-1
`electron mag. mom. anomaly` | 0.00115965218046
`electron mag. mom. to Bohr magneton ratio` | -1.00115965218046
`electron mag. mom. to nuclear magneton ratio` | -1838.281971877
`electron mass` | 9.1093837139e-31 kg
`electron mass energy equivalent` | 8.187105788e-14 J
`electron mass energy equivalent in MeV` | 0.51099895069 MeV
`electron mass in u` | 0.0005485799090441 u
`electron molar mass` | 5.4857990962e-07 kg mol^-1
`electron relative atomic mass` | 0.0005485799090441
`electron to alpha particle mass ratio` | 0.0001370933554733
`electron to shielded helion mag. mom. ratio` | 864.05823986
`electron to shielded proton mag. mom. ratio` | -658.2275856
`electron volt` | 1.602176634e-19 J
`electron volt-atomic mass unit relationship` | 1.07354410083e-09 u
`electron volt-hartree relationship` | 0.036749322175665 E_h
`electron volt-hertz relationship` | 241798924208491.8 Hz
`electron volt-inverse meter relationship` | 806554.3937349211 m^-1
`electron volt-joule relationship` | 1.602176634e-19 J
`electron volt-kelvin relationship` | 11604.518121550082 K
`electron volt-kilogram relationship` | 1.7826619216278975e-36 kg
`electron-deuteron mag. mom. ratio` | -2143.9234921
`electron-deuteron mass ratio` | 0.0002724437107629
`electron-helion mass ratio` | 0.0001819543074649
`electron-muon mag. mom. ratio` | 206.7669881
`electron-muon mass ratio` | 0.0048363317
`electron-neutron mag. mom. ratio` | 960.92048
`electron-neutron mass ratio` | 0.00054386734416
`electron-proton mag. mom. ratio` | -658.21068789
`electron-proton mass ratio` | 0.0005446170214889
`electron-tau mass ratio` | 0.000287585
`electron-triton mass ratio` | 0.0001819200062327
`elementary charge` | 1.602176634e-19 C
`elementary charge over h-bar` | 1519267447878626.0 A J^-1
`Faraday constant` | 96485.33212331001 C mol^-1
`Fermi coupling constant` | 1.1663787e-05 GeV^-2
`fine-structure constant` | 0.0072973525643
`first radiation constant` | 3.7417718521927573e-16 W m^2
`first radiation constant for spectral radiance` | 1.1910429723971884e-16 W m^2 sr^-1
`Hartree energy` | 4.359744722206e-18 J
`Hartree energy in eV` | 27.211386245981 eV
`hartree-atomic mass unit relationship` | 2.92126231797e-08 u
`hartree-electron volt relationship` | 27.211386245981 eV
`hartree-hertz relationship` | 6579683920499900.0 Hz
`hartree-inverse meter relationship` | 21947463.136314 m^-1
`hartree-joule relationship` | 4.359744722206e-18 J
`hartree-kelvin relationship` | 315775.02480398 K
`hartree-kilogram relationship` | 4.8508702095419e-35 kg
`helion g factor` | -4.2552506995
`helion mag. mom.` | -1.07461755198e-26 J T^-1
`helion mag. mom. to Bohr magneton ratio` | -0.00115874098083
`helion mag. mom. to nuclear magneton ratio` | -2.1276253498
`helion mass` | 5.0064127862e-27 kg
`helion mass energy equivalent` | 4.4995394185e-10 J
`helion mass energy equivalent in MeV` | 2808.39161112 MeV
`helion mass in u` | 3.014932246932 u
`helion molar mass` | 0.0030149322501 kg mol^-1
`helion relative atomic mass` | 3.014932246932
`helion shielding shift` | 5.9967029e-05
`helion-electron mass ratio` | 5495.88527984
`helion-proton mass ratio` | 2.993152671552
`hertz-atomic mass unit relationship` | 4.439821659e-24 u
`hertz-electron volt relationship` | 4.135667696923859e-15 eV
`hertz-hartree relationship` | 1.5198298460574e-16 E_h
`hertz-inverse meter relationship` | 3.3356409519815204e-09 m^-1
`hertz-joule relationship` | 6.62607015e-34 J
`hertz-kelvin relationship` | 4.799243073366221e-11 K
`hertz-kilogram relationship` | 7.372497323812708e-51 kg
`hyperfine transition frequency of Cs-133` | 9192631770.0 Hz
`inverse fine-structure constant` | 137.035999177
`inverse meter-atomic mass unit relationship` | 1.33102504824e-15 u
`inverse meter-electron volt relationship` | 1.2398419843320026e-06 eV
`inverse meter-hartree relationship` | 4.5563352529132e-08 E_h
`inverse meter-hertz relationship` | 299792458.0 Hz
`inverse meter-joule relationship` | 1.9864458571489286e-25 J
`inverse meter-kelvin relationship` | 0.014387768775039337 K
`inverse meter-kilogram relationship` | 2.2102190943042335e-42 kg
`inverse of conductance quantum` | 12906.403729652257 ohm
`Josephson constant` | 483597848416983.6 Hz V^-1
`joule-atomic mass unit relationship` | 6700535247.1 u
`joule-electron volt relationship` | 6.241509074460763e+18 eV
`joule-hartree relationship` | 2.2937122783969e+17 E_h
`joule-hertz relationship` | 1.5091901796421518e+33 Hz
`joule-inverse meter relationship` | 5.03411656754271e+24 m^-1
`joule-kelvin relationship` | 7.24297051603992e+22 K
`joule-kilogram relationship` | 1.1126500560536185e-17 kg
`kelvin-atomic mass unit relationship` | 9.2510872884e-14 u
`kelvin-electron volt relationship` | 8.617333262145179e-05 eV
`kelvin-hartree relationship` | 3.1668115634564e-06 E_h
`kelvin-hertz relationship` | 20836619123.327576 Hz
`kelvin-inverse meter relationship` | 69.50348004861274 m^-1
`kelvin-joule relationship` | 1.380649e-23 J
`kelvin-kilogram relationship` | 1.5361791872403723e-40 kg
`kilogram-atomic mass unit relationship` | 6.0221407537e+26 u
`kilogram-electron volt relationship` | 5.609588603804452e+35 eV
`kilogram-hartree relationship` | 2.0614857887415e+34 E_h
`kilogram-hertz relationship` | 1.3563924896521321e+50 Hz
`kilogram-inverse meter relationship` | 4.524438335443823e+41 m^-1
`kilogram-joule relationship` | 8.987551787368176e+16 J
`kilogram-kelvin relationship` | 6.509657260728958e+39 K
`lattice parameter of silicon` | 5.431020511e-10 m
`lattice spacing of ideal Si (220)` | 1.920155716e-10 m
`Loschmidt constant (273.15 K, 100 kPa)` | 2.6516458048837345e+25 m^-3
`Loschmidt constant (273.15 K, 101.325 kPa)` | 2.686780111798444e+25 m^-3
`luminous efficacy` | 683.0 lm W^-1
`mag. flux quantum` | 2.0678338484619295e-15 Wb
`molar gas constant` | 8.31446261815324 J mol^-1 K^-1
`molar mass constant` | 0.00100000000105 kg mol^-1
`molar mass of carbon-12` | 0.0120000000126 kg mol^-1
`molar Planck constant` | 3.990312712893431e-10 J Hz^-1 mol^-1
`molar volume of ideal gas (273.15 K, 100 kPa)` | 0.02271095464148557 m^3 mol^-1
`molar volume of ideal gas (273.15 K, 101.325 kPa)` | 0.022413969545014137 m^3 mol^-1
`molar volume of silicon` | 1.205883199e-05 m^3 mol^-1
`Molybdenum x unit` | 1.00209952e-13 m
`muon Compton wavelength` | 1.17344411e-14 m
`muon g factor` | -2.00233184123
`muon mag. mom.` | -4.4904483e-26 J T^-1
`muon mag. mom. anomaly` | 0.00116592062
`muon mag. mom. to Bohr magneton ratio` | -0.00484197048
`muon mag. mom. to nuclear magneton ratio` | -8.89059704
`muon mass` | 1.883531627e-28 kg
`muon mass energy equivalent` | 1.692833804e-11 J
`muon mass energy equivalent in MeV` | 105.6583755 MeV
`muon mass in u` | 0.1134289257 u
`muon molar mass` | 0.0001134289258 kg mol^-1
`muon-electron mass ratio` | 206.7682827
`muon-neutron mass ratio` | 0.1124545168
`muon-proton mag. mom. ratio` | -3.183345146
`muon-proton mass ratio` | 0.1126095262
`muon-tau mass ratio` | 0.0594635
`natural unit of action` | 1.0545718176461565e-34 J s
`natural unit of action in eV s` | 6.582119569509067e-16 eV s
`natural unit of energy` | 8.187105788e-14 J
`natural unit of energy in MeV` | 0.51099895069 MeV
`natural unit of length` | 3.8615926744e-13 m
`natural unit of mass` | 9.1093837139e-31 kg
`natural unit of momentum` | 2.730924488e-22 kg m s^-1
`natural unit of momentum in MeV/c` | 0.5109989461 MeV/c
`natural unit of time` | 1.28808866644e-21 s
`natural unit of velocity` | 299792458.0 m s^-1
`neutron Compton wavelength` | 1.31959090382e-15 m
`neutron g factor` | -3.82608552
`neutron gyromag. ratio` | 183247174.0 s^-1 T^-1
`neutron gyromag. ratio in MHz/T` | 29.1646935 MHz T^-1
`neutron mag. mom.` | -9.6623653e-27 J T^-1
`neutron mag. mom. to Bohr magneton ratio` | -0.00104187565
`neutron mag. mom. to nuclear magneton ratio` | -1.91304276
`neutron mass` | 1.67492750056e-27 kg
`neutron mass energy equivalent` | 1.50534976514e-10 J
`neutron mass energy equivalent in MeV` | 939.56542194 MeV
`neutron mass in u` | 1.00866491606 u
`neutron molar mass` | 0.00100866491712 kg mol^-1
`neutron relative atomic mass` | 1.00866491606
`neutron to shielded proton mag. mom. ratio` | -0.68499694
`neutron-electron mag. mom. ratio` | 0.00104066884
`neutron-electron mass ratio` | 1838.683662
`neutron-muon mass ratio` | 8.89248408
`neutron-proton mag. mom. ratio` | -0.68497935
`neutron-proton mass difference` | 2.30557461e-30 kg
`neutron-proton mass difference energy equivalent` | 2.07214712e-13 J
`neutron-proton mass difference energy equivalent in MeV` | 1.29333251 MeV
`neutron-proton mass difference in u` | 0.00138844948 u
`neutron-proton mass ratio` | 1.00137841946
`neutron-tau mass ratio` | 0.528779
`Newtonian constant of gravitation` | 6.6743e-11 m^3 kg^-1 s^-2
`Newtonian constant of gravitation over h-bar c` | 6.70883e-39 (GeV/c^2)^-2
`nuclear magneton` | 5.0507837393e-27 J T^-1
`nuclear magneton in eV/T` | 3.15245125417e-08 eV T^-1
`nuclear magneton in inverse meter per tesla` | 0.0254262341009 m^-1 T^-1
`nuclear magneton in K/T` | 0.00036582677706 K T^-1
`nuclear magneton in MHz/T` | 7.6225932188 MHz T^-1
`Planck constant` | 6.62607015e-34 J Hz^-1
`Planck constant in eV/Hz` | 4.135667696923859e-15 eV Hz^-1
`Planck length` | 1.616255e-35 m
`Planck mass` | 2.176434e-08 kg
`Planck mass energy equivalent in GeV` | 1.22089e+19 GeV
`Planck temperature` | 1.416784e+32 K
`Planck time` | 5.391247e-44 s
`proton charge to mass quotient` | 95788331.43 C kg^-1
`proton Compton wavelength` | 1.3214098536e-15 m
`proton g factor` | 5.5856946893
`proton gyromag. ratio` | 267522187.08 s^-1 T^-1
`proton gyromag. ratio in MHz/T` | 42.577478461 MHz T^-1
`proton mag. mom.` | 1.41060679545e-26 J T^-1
`proton mag. mom. to Bohr magneton ratio` | 0.0015210322023
`proton mag. mom. to nuclear magneton ratio` | 2.79284734463
`proton mag. shielding correction` | 2.56715e-05
`proton mass` | 1.67262192595e-27 kg
`proton mass energy equivalent` | 1.50327761802e-10 J
`proton mass energy equivalent in MeV` | 938.27208943 MeV
`proton mass in u` | 1.0072764665789 u
`proton molar mass` | 0.00100727646764 kg mol^-1
`proton relative atomic mass` | 1.0072764665789
`proton rms charge radius` | 8.4075e-16 m
`proton-electron mass ratio` | 1836.152673426
`proton-muon mass ratio` | 8.88024338
`proton-neutron mag. mom. ratio` | -1.45989802
`proton-neutron mass ratio` | 0.99862347797
`proton-tau mass ratio` | 0.528051
`quantum of circulation` | 0.00036369475467 m^2 s^-1
`quantum of circulation times 2` | 0.00072738950934 m^2 s^-1
`reduced Compton wavelength` | 3.8615926744e-13 m
`reduced muon Compton wavelength` | 1.867594306e-15 m
`reduced neutron Compton wavelength` | 2.100194152e-16 m
`reduced Planck constant` | 1.0545718176461565e-34 J s
`reduced Planck constant in eV s` | 6.582119569509067e-16 eV s
`reduced Planck constant times c in MeV fm` | 197.3269804593025 MeV fm
`reduced proton Compton wavelength` | 2.10308910051e-16 m
`reduced tau Compton wavelength` | 1.110538e-16 m
`Rydberg constant` | 10973731.568157 m^-1
`Rydberg constant times c in Hz` | 3289841960250000.0 Hz
`Rydberg constant times hc in eV` | 13.60569312299 eV
`Rydberg constant times hc in J` | 2.179872361103e-18 J
`Sackur-Tetrode constant (1 K, 100 kPa)` | -1.15170753496
`Sackur-Tetrode constant (1 K, 101.325 kPa)` | -1.16487052149
`second radiation constant` | 0.014387768775039337 m K
`shielded helion gyromag. ratio` | 203789460.78 s^-1 T^-1
`shielded helion gyromag. ratio in MHz/T` | 32.434100033 MHz T^-1
`shielded helion mag. mom.` | -1.07455311035e-26 J T^-1
`shielded helion mag. mom. to Bohr magneton ratio` | -0.00115867149457
`shielded helion mag. mom. to nuclear magneton ratio` | -2.1274977624
`shielded helion to proton mag. mom. ratio` | -0.76176657721
`shielded helion to shielded proton mag. mom. ratio` | -0.7617861334
`shielded proton gyromag. ratio` | 267515319.4 s^-1 T^-1
`shielded proton gyromag. ratio in MHz/T` | 42.57638543 MHz T^-1
`shielded proton mag. mom.` | 1.410570583e-26 J T^-1
`shielded proton mag. mom. to Bohr magneton ratio` | 0.0015209931551
`shielded proton mag. mom. to nuclear magneton ratio` | 2.792775648
`shielding difference of d and p in HD` | 1.9877e-08
`shielding difference of t and p in HT` | 2.3945e-08
`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` | 5.6703744191844314e-08 W m^-2 K^-4
`tau Compton wavelength` | 6.97771e-16 m
`tau energy equivalent` | 1776.86 MeV
`tau mass` | 3.16754e-27 kg
`tau mass energy equivalent` | 2.84684e-10 J
`tau mass in u` | 1.90754 u
`tau molar mass` | 0.00190754 kg mol^-1
`tau-electron mass ratio` | 3477.23
`tau-muon mass ratio` | 16.817
`tau-neutron mass ratio` | 1.89115
`tau-proton mass ratio` | 1.89376
`Thomson cross section` | 6.6524587051e-29 m^2
`triton g factor` | 5.95792493
`triton mag. mom.` | 1.5046095178e-26 J T^-1
`triton mag. mom. to Bohr magneton ratio` | 0.0016223936648
`triton mag. mom. to nuclear magneton ratio` | 2.978962465
`triton mass` | 5.0073567512e-27 kg
`triton mass energy equivalent` | 4.5003878119e-10 J
`triton mass energy equivalent in MeV` | 2808.92113668 MeV
`triton mass in u` | 3.01550071597 u
`triton molar mass` | 0.00301550071913 kg mol^-1
`triton relative atomic mass` | 3.01550071597
`triton to proton mag. mom. ratio` | 1.0666399189
`triton-electron mass ratio` | 5496.92153551
`triton-proton mass ratio` | 2.99371703403
`unified atomic mass unit` | 1.66053906892e-27 kg
`vacuum electric permittivity` | 8.8541878188e-12 F m^-1
`vacuum mag. permeability` | 1.25663706127e-06 N A^-2
`von Klitzing constant` | 25812.807459304513 ohm
`W to Z mass ratio` | 0.88145
`weak mixing angle` | 0.22305
`Wien frequency displacement law constant` | 58789257576.468254 Hz K^-1
`Wien wavelength displacement law constant` | 0.0028977719551851727 m K

## Units

### SI prefixes

`quetta` | \(10^{30}\)
`ronna` | \(10^{27}\)
`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` | \(10^{-21}\)
`yocto` | \(10^{-24}\)
`ronto` | \(10^{-27}\)
`quecto` | \(10^{-30}\)

### 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.

### 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

[CODATA2022]

CODATA Recommended Values of the Fundamental Physical Constants 2022.

https://physics.nist.gov/cuu/Constants/