# 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 2018 CODATA recommended values [CODATA2018] 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` | 6.6446573357e-27 kg
`alpha particle mass energy equivalent` | 5.9719201914e-10 J
`alpha particle mass energy equivalent in MeV` | 3727.3794066 MeV
`alpha particle mass in u` | 4.001506179127 u
`alpha particle molar mass` | 0.0040015061777 kg mol^-1
`alpha particle relative atomic mass` | 4.001506179127
`alpha particle-electron mass ratio` | 7294.29954142
`alpha particle-proton mass ratio` | 3.97259969009
`Angstrom star` | 1.00001495e-10 m
`atomic mass constant` | 1.6605390666e-27 kg
`atomic mass constant energy equivalent` | 1.4924180856e-10 J
`atomic mass constant energy equivalent in MeV` | 931.49410242 MeV
`atomic mass unit-electron volt relationship` | 931494102.42 eV
`atomic mass unit-hartree relationship` | 34231776.874 E_h
`atomic mass unit-hertz relationship` | 2.25234271871e+23 Hz
`atomic mass unit-inverse meter relationship` | 751300661040000.0 m^-1
`atomic mass unit-joule relationship` | 1.4924180856e-10 J
`atomic mass unit-kelvin relationship` | 10809540191600.0 K
`atomic mass unit-kilogram relationship` | 1.6605390666e-27 kg
`atomic unit of 1st hyperpolarizability` | 3.2063613061e-53 C^3 m^3 J^-2
`atomic unit of 2nd hyperpolarizability` | 6.2353799905e-65 C^4 m^4 J^-3
`atomic unit of action` | 1.054571817e-34 J s
`atomic unit of charge` | 1.602176634e-19 C
`atomic unit of charge density` | 1081202384570.0 C m^-3
`atomic unit of current` | 0.00662361823751 A
`atomic unit of electric dipole mom.` | 8.4783536255e-30 C m
`atomic unit of electric field` | 514220674763.0 V m^-1
`atomic unit of electric field gradient` | 9.7173624292e+21 V m^-2
`atomic unit of electric polarizability` | 1.64877727436e-41 C^2 m^2 J^-1
`atomic unit of electric potential` | 27.211386245988 V
`atomic unit of electric quadrupole mom.` | 4.4865515246e-40 C m^2
`atomic unit of energy` | 4.3597447222071e-18 J
`atomic unit of force` | 8.2387234983e-08 N
`atomic unit of length` | 5.29177210903e-11 m
`atomic unit of mag. dipole mom.` | 1.85480201566e-23 J T^-1
`atomic unit of mag. flux density` | 235051.756758 T
`atomic unit of magnetizability` | 7.8910366008e-29 J T^-2
`atomic unit of mass` | 9.1093837015e-31 kg
`atomic unit of momentum` | 1.9928519141e-24 kg m s^-1
`atomic unit of permittivity` | 1.11265005545e-10 F m^-1
`atomic unit of time` | 2.4188843265857e-17 s
`atomic unit of velocity` | 2187691.26364 m s^-1
`Avogadro constant` | 6.02214076e+23 mol^-1
`Bohr magneton` | 9.2740100783e-24 J T^-1
`Bohr magneton in eV/T` | 5.788381806e-05 eV T^-1
`Bohr magneton in Hz/T` | 13996244936.1 Hz T^-1
`Bohr magneton in inverse meter per tesla` | 46.686447783 m^-1 T^-1
`Bohr magneton in K/T` | 0.67171381563 K T^-1
`Bohr radius` | 5.29177210903e-11 m
`Boltzmann constant` | 1.380649e-23 J K^-1
`Boltzmann constant in eV/K` | 8.617333262e-05 eV K^-1
`Boltzmann constant in Hz/K` | 20836619120.0 Hz K^-1
`Boltzmann constant in inverse meter per kelvin` | 69.50348004 m^-1 K^-1
`characteristic impedance of vacuum` | 376.730313668 ohm
`classical electron radius` | 2.8179403262e-15 m
`Compton wavelength` | 2.42631023867e-12 m
`conductance quantum` | 7.748091729e-05 S
`conventional value of ampere-90` | 1.00000008887 A
`conventional value of coulomb-90` | 1.00000008887 C
`conventional value of farad-90` | 0.9999999822 F
`conventional value of henry-90` | 1.00000001779 H
`conventional value of Josephson constant` | 483597900000000.0 Hz V^-1
`conventional value of ohm-90` | 1.00000001779 ohm
`conventional value of volt-90` | 1.00000010666 V
`conventional value of von Klitzing constant` | 25812.807 ohm
`conventional value of watt-90` | 1.00000019553 W
`Cu x unit` | 1.00207697e-13 m
`deuteron g factor` | 0.8574382338
`deuteron mag. mom.` | 4.330735094e-27 J T^-1
`deuteron mag. mom. to Bohr magneton ratio` | 0.000466975457
`deuteron mag. mom. to nuclear magneton ratio` | 0.8574382338
`deuteron mass` | 3.3435837724e-27 kg
`deuteron mass energy equivalent` | 3.00506323102e-10 J
`deuteron mass energy equivalent in MeV` | 1875.61294257 MeV
`deuteron mass in u` | 2.013553212745 u
`deuteron molar mass` | 0.00201355321205 kg mol^-1
`deuteron relative atomic mass` | 2.013553212745
`deuteron rms charge radius` | 2.12799e-15 m
`deuteron-electron mag. mom. ratio` | -0.0004664345551
`deuteron-electron mass ratio` | 3670.48296788
`deuteron-neutron mag. mom. ratio` | -0.44820653
`deuteron-proton mag. mom. ratio` | 0.30701220939
`deuteron-proton mass ratio` | 1.99900750139
`electron charge to mass quotient` | -175882001076.0 C kg^-1
`electron g factor` | -2.00231930436256
`electron gyromag. ratio` | 176085963023.0 s^-1 T^-1
`electron gyromag. ratio in MHz/T` | 28024.9514242 MHz T^-1
`electron mag. mom.` | -9.2847647043e-24 J T^-1
`electron mag. mom. anomaly` | 0.00115965218128
`electron mag. mom. to Bohr magneton ratio` | -1.00115965218128
`electron mag. mom. to nuclear magneton ratio` | -1838.28197188
`electron mass` | 9.1093837015e-31 kg
`electron mass energy equivalent` | 8.1871057769e-14 J
`electron mass energy equivalent in MeV` | 0.51099895 MeV
`electron mass in u` | 0.000548579909065 u
`electron molar mass` | 5.4857990888e-07 kg mol^-1
`electron relative atomic mass` | 0.000548579909065
`electron to alpha particle mass ratio` | 0.0001370933554787
`electron to shielded helion mag. mom. ratio` | 864.058257
`electron to shielded proton mag. mom. ratio` | -658.2275971
`electron volt` | 1.602176634e-19 J
`electron volt-atomic mass unit relationship` | 1.07354410233e-09 u
`electron volt-hartree relationship` | 0.036749322175655 E_h
`electron volt-hertz relationship` | 241798924200000.0 Hz
`electron volt-inverse meter relationship` | 806554.3937 m^-1
`electron volt-joule relationship` | 1.602176634e-19 J
`electron volt-kelvin relationship` | 11604.51812 K
`electron volt-kilogram relationship` | 1.782661921e-36 kg
`electron-deuteron mag. mom. ratio` | -2143.9234915
`electron-deuteron mass ratio` | 0.0002724437107462
`electron-helion mass ratio` | 0.0001819543074573
`electron-muon mag. mom. ratio` | 206.7669883
`electron-muon mass ratio` | 0.00483633169
`electron-neutron mag. mom. ratio` | 960.9205
`electron-neutron mass ratio` | 0.00054386734424
`electron-proton mag. mom. ratio` | -658.21068789
`electron-proton mass ratio` | 0.000544617021487
`electron-tau mass ratio` | 0.000287585
`electron-triton mass ratio` | 0.0001819200062251
`elementary charge` | 1.602176634e-19 C
`elementary charge over h-bar` | 1519267447000000.0 A J^-1
`Faraday constant` | 96485.33212 C mol^-1
`Fermi coupling constant` | 1.1663787e-05 GeV^-2
`fine-structure constant` | 0.0072973525693
`first radiation constant` | 3.741771852e-16 W m^2
`first radiation constant for spectral radiance` | 1.191042972e-16 W m^2 sr^-1
`Hartree energy` | 4.3597447222071e-18 J
`Hartree energy in eV` | 27.211386245988 eV
`hartree-atomic mass unit relationship` | 2.92126232205e-08 u
`hartree-electron volt relationship` | 27.211386245988 eV
`hartree-hertz relationship` | 6579683920502000.0 Hz
`hartree-inverse meter relationship` | 21947463.13632 m^-1
`hartree-joule relationship` | 4.3597447222071e-18 J
`hartree-kelvin relationship` | 315775.02480407 K
`hartree-kilogram relationship` | 4.8508702095432e-35 kg
`helion g factor` | -4.255250615
`helion mag. mom.` | -1.074617532e-26 J T^-1
`helion mag. mom. to Bohr magneton ratio` | -0.001158740958
`helion mag. mom. to nuclear magneton ratio` | -2.127625307
`helion mass` | 5.0064127796e-27 kg
`helion mass energy equivalent` | 4.4995394125e-10 J
`helion mass energy equivalent in MeV` | 2808.39160743 MeV
`helion mass in u` | 3.014932247175 u
`helion molar mass` | 0.00301493224613 kg mol^-1
`helion relative atomic mass` | 3.014932247175
`helion shielding shift` | 5.996743e-05
`helion-electron mass ratio` | 5495.88528007
`helion-proton mass ratio` | 2.99315267167
`hertz-atomic mass unit relationship` | 4.4398216652e-24 u
`hertz-electron volt relationship` | 4.135667696e-15 eV
`hertz-hartree relationship` | 1.519829846057e-16 E_h
`hertz-inverse meter relationship` | 3.3356409519815204e-09 m^-1
`hertz-joule relationship` | 6.62607015e-34 J
`hertz-kelvin relationship` | 4.799243073e-11 K
`hertz-kilogram relationship` | 7.372497323e-51 kg
`hyperfine transition frequency of Cs-133` | 9192631770.0 Hz
`inverse fine-structure constant` | 137.035999084
`inverse meter-atomic mass unit relationship` | 1.3310250501e-15 u
`inverse meter-electron volt relationship` | 1.239841984e-06 eV
`inverse meter-hartree relationship` | 4.556335252912e-08 E_h
`inverse meter-hertz relationship` | 299792458.0 Hz
`inverse meter-joule relationship` | 1.986445857e-25 J
`inverse meter-kelvin relationship` | 0.01438776877 K
`inverse meter-kilogram relationship` | 2.210219094e-42 kg
`inverse of conductance quantum` | 12906.40372 ohm
`Josephson constant` | 483597848400000.0 Hz V^-1
`joule-atomic mass unit relationship` | 6700535256.5 u
`joule-electron volt relationship` | 6.241509074e+18 eV
`joule-hartree relationship` | 2.2937122783963e+17 E_h
`joule-hertz relationship` | 1.509190179e+33 Hz
`joule-inverse meter relationship` | 5.034116567e+24 m^-1
`joule-kelvin relationship` | 7.242970516e+22 K
`joule-kilogram relationship` | 1.1126500560536185e-17 kg
`kelvin-atomic mass unit relationship` | 9.2510873014e-14 u
`kelvin-electron volt relationship` | 8.617333262e-05 eV
`kelvin-hartree relationship` | 3.1668115634556e-06 E_h
`kelvin-hertz relationship` | 20836619120.0 Hz
`kelvin-inverse meter relationship` | 69.50348004 m^-1
`kelvin-joule relationship` | 1.380649e-23 J
`kelvin-kilogram relationship` | 1.536179187e-40 kg
`kilogram-atomic mass unit relationship` | 6.0221407621e+26 u
`kilogram-electron volt relationship` | 5.609588603e+35 eV
`kilogram-hartree relationship` | 2.0614857887409e+34 E_h
`kilogram-hertz relationship` | 1.356392489e+50 Hz
`kilogram-inverse meter relationship` | 4.524438335e+41 m^-1
`kilogram-joule relationship` | 8.987551787368176e+16 J
`kilogram-kelvin relationship` | 6.50965726e+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)` | 2.651645804e+25 m^-3
`Loschmidt constant (273.15 K, 101.325 kPa)` | 2.686780111e+25 m^-3
`luminous efficacy` | 683.0 lm W^-1
`mag. flux quantum` | 2.067833848e-15 Wb
`Mo x unit` | 1.00209952e-13 m
`molar gas constant` | 8.314462618 J mol^-1 K^-1
`molar mass constant` | 0.00099999999965 kg mol^-1
`molar mass of carbon-12` | 0.0119999999958 kg mol^-1
`molar Planck constant` | 3.990312712e-10 J Hz^-1 mol^-1
`molar volume of ideal gas (273.15 K, 100 kPa)` | 0.02271095464 m^3 mol^-1
`molar volume of ideal gas (273.15 K, 101.325 kPa)` | 0.02241396954 m^3 mol^-1
`molar volume of silicon` | 1.205883199e-05 m^3 mol^-1
`muon Compton wavelength` | 1.17344411e-14 m
`muon g factor` | -2.0023318418
`muon mag. mom.` | -4.4904483e-26 J T^-1
`muon mag. mom. anomaly` | 0.00116592089
`muon mag. mom. to Bohr magneton ratio` | -0.00484197047
`muon mag. mom. to nuclear magneton ratio` | -8.89059703
`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` | 0.1134289259 u
`muon molar mass` | 0.0001134289259 kg mol^-1
`muon-electron mass ratio` | 206.768283
`muon-neutron mass ratio` | 0.112454517
`muon-proton mag. mom. ratio` | -3.183345142
`muon-proton mass ratio` | 0.1126095264
`muon-tau mass ratio` | 0.0594635
`natural unit of action` | 1.054571817e-34 J s
`natural unit of action in eV s` | 6.582119569e-16 eV s
`natural unit of energy` | 8.1871057769e-14 J
`natural unit of energy in MeV` | 0.51099895 MeV
`natural unit of length` | 3.8615926796e-13 m
`natural unit of mass` | 9.1093837015e-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` | 1.28808866819e-21 s
`natural unit of velocity` | 299792458.0 m s^-1
`neutron Compton wavelength` | 1.31959090581e-15 m
`neutron g factor` | -3.82608545
`neutron gyromag. ratio` | 183247171.0 s^-1 T^-1
`neutron gyromag. ratio in MHz/T` | 29.1646931 MHz T^-1
`neutron mag. mom.` | -9.6623651e-27 J T^-1
`neutron mag. mom. to Bohr magneton ratio` | -0.00104187563
`neutron mag. mom. to nuclear magneton ratio` | -1.91304273
`neutron mass` | 1.67492749804e-27 kg
`neutron mass energy equivalent` | 1.50534976287e-10 J
`neutron mass energy equivalent in MeV` | 939.56542052 MeV
`neutron mass in u` | 1.00866491595 u
`neutron molar mass` | 0.0010086649156 kg mol^-1
`neutron relative atomic mass` | 1.00866491595
`neutron to shielded proton mag. mom. ratio` | -0.68499694
`neutron-electron mag. mom. ratio` | 0.00104066882
`neutron-electron mass ratio` | 1838.68366173
`neutron-muon mass ratio` | 8.89248406
`neutron-proton mag. mom. ratio` | -0.68497934
`neutron-proton mass difference` | 2.30557435e-30 kg
`neutron-proton mass difference energy equivalent` | 2.07214689e-13 J
`neutron-proton mass difference energy equivalent in MeV` | 1.29333236 MeV
`neutron-proton mass difference in u` | 0.00138844933 u
`neutron-proton mass ratio` | 1.00137841931
`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` | 5.0507837461e-27 J T^-1
`nuclear magneton in eV/T` | 3.15245125844e-08 eV T^-1
`nuclear magneton in inverse meter per tesla` | 0.0254262341353 m^-1 T^-1
`nuclear magneton in K/T` | 0.00036582677756 K T^-1
`nuclear magneton in MHz/T` | 7.6225932291 MHz T^-1
`Planck constant` | 6.62607015e-34 J Hz^-1
`Planck constant in eV/Hz` | 4.135667696e-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` | 95788331.56 C kg^-1
`proton Compton wavelength` | 1.32140985539e-15 m
`proton g factor` | 5.5856946893
`proton gyromag. ratio` | 267522187.44 s^-1 T^-1
`proton gyromag. ratio in MHz/T` | 42.577478518 MHz T^-1
`proton mag. mom.` | 1.41060679736e-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` | 2.5689e-05
`proton mass` | 1.67262192369e-27 kg
`proton mass energy equivalent` | 1.50327761598e-10 J
`proton mass energy equivalent in MeV` | 938.27208816 MeV
`proton mass in u` | 1.007276466621 u
`proton molar mass` | 0.00100727646627 kg mol^-1
`proton relative atomic mass` | 1.007276466621
`proton rms charge radius` | 8.414e-16 m
`proton-electron mass ratio` | 1836.15267343
`proton-muon mass ratio` | 8.88024337
`proton-neutron mag. mom. ratio` | -1.45989805
`proton-neutron mass ratio` | 0.99862347812
`proton-tau mass ratio` | 0.528051
`quantum of circulation` | 0.00036369475516 m^2 s^-1
`quantum of circulation times 2` | 0.00072738951032 m^2 s^-1
`reduced Compton wavelength` | 3.8615926796e-13 m
`reduced muon Compton wavelength` | 1.867594306e-15 m
`reduced neutron Compton wavelength` | 2.1001941552e-16 m
`reduced Planck constant` | 1.054571817e-34 J s
`reduced Planck constant in eV s` | 6.582119569e-16 eV s
`reduced Planck constant times c in MeV fm` | 197.3269804 MeV fm
`reduced proton Compton wavelength` | 2.10308910336e-16 m
`reduced tau Compton wavelength` | 1.110538e-16 m
`Rydberg constant` | 10973731.56816 m^-1
`Rydberg constant times c in Hz` | 3289841960250800.0 Hz
`Rydberg constant times hc in eV` | 13.605693122994 eV
`Rydberg constant times hc in J` | 2.1798723611035e-18 J
`Sackur-Tetrode constant (1 K, 100 kPa)` | -1.15170753706
`Sackur-Tetrode constant (1 K, 101.325 kPa)` | -1.16487052358
`second radiation constant` | 0.01438776877 m K
`shielded helion gyromag. ratio` | 203789456.9 s^-1 T^-1
`shielded helion gyromag. ratio in MHz/T` | 32.43409942 MHz T^-1
`shielded helion mag. mom.` | -1.07455309e-26 J T^-1
`shielded helion mag. mom. to Bohr magneton ratio` | -0.001158671471
`shielded helion mag. mom. to nuclear magneton ratio` | -2.127497719
`shielded helion to proton mag. mom. ratio` | -0.7617665618
`shielded helion to shielded proton mag. mom. ratio` | -0.7617861313
`shielded proton gyromag. ratio` | 267515315.1 s^-1 T^-1
`shielded proton gyromag. ratio in MHz/T` | 42.57638474 MHz T^-1
`shielded proton mag. mom.` | 1.41057056e-26 J T^-1
`shielded proton mag. mom. to Bohr magneton ratio` | 0.001520993128
`shielded proton mag. mom. to nuclear magneton ratio` | 2.792775599
`shielding difference of d and p in HD` | 2.02e-08
`shielding difference of t and p in HT` | 2.414e-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` | 5.670374419e-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` | 6.6524587321e-29 m^2
`triton g factor` | 5.957924931
`triton mag. mom.` | 1.5046095202e-26 J T^-1
`triton mag. mom. to Bohr magneton ratio` | 0.0016223936651
`triton mag. mom. to nuclear magneton ratio` | 2.9789624656
`triton mass` | 5.0073567446e-27 kg
`triton mass energy equivalent` | 4.500387806e-10 J
`triton mass energy equivalent in MeV` | 2808.92113298 MeV
`triton mass in u` | 3.01550071621 u
`triton molar mass` | 0.00301550071517 kg mol^-1
`triton relative atomic mass` | 3.01550071621
`triton to proton mag. mom. ratio` | 1.0666399191
`triton-electron mass ratio` | 5496.92153573
`triton-proton mass ratio` | 2.99371703414
`unified atomic mass unit` | 1.6605390666e-27 kg
`vacuum electric permittivity` | 8.8541878128e-12 F m^-1
`vacuum mag. permeability` | 1.25663706212e-06 N A^-2
`von Klitzing constant` | 25812.80745 ohm
`W to Z mass ratio` | 0.88153
`weak mixing angle` | 0.2229
`Wien frequency displacement law constant` | 58789257570.0 Hz K^-1
`Wien wavelength displacement law constant` | 0.002897771955 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

[CODATA2018]

CODATA Recommended Values of the Fundamental Physical Constants 2018.

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