### Table Of Contents

- Constants (`scipy.constants`)
  - Mathematical constants
  - Physical constants
    - Constants database
  - Units
    - SI prefixes
    - Binary prefixes
    - Weight
    - Angle
    - Time
    - Length
    - Pressure
    - Area
    - Volume
    - Speed
    - Temperature
    - Energy
    - Power
    - Force
    - Optics
  - References

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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

`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` | \(2^{80}\)

### Weight

`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
`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

`C2K`(C) | Convert Celsius to Kelvin
`K2C`(K) | Convert Kelvin to Celsius
`F2C`(F) | Convert Fahrenheit to Celsius
`C2F`(C) | Convert Celsius to Fahrenheit
`F2K`(F) | Convert Fahrenheit to Kelvin
`K2F`(K) | Convert Kelvin to Fahrenheit

### 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