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# Constants (`scipy.constants`)

Physical and mathematical constants and units.

## Mathematical constants

`pi` | Pi
`golden` | Golden ratio

## Physical constants

`c` | speed of light in vacuum
`mu_0` | the magnetic constant
`epsilon_0` | the electric constant (vacuum permittivity),
`h` | the Planck constant
`hbar` |
`G` | Newtonian constant of gravitation
`g` | standard acceleration of gravity
`e` | elementary charge
`R` | molar gas constant
`alpha` | fine-structure constant
`N_A` | Avogadro constant
`k` | Boltzmann constant
`sigma` | Stefan-Boltzmann constant
`Wien` | Wien displacement law constant
`Rydberg` | Rydberg constant
`m_e` | electron mass
`m_p` | proton mass
`m_n` | neutron mass

### Constants database

In addition to the above variables, `scipy.constants` also contains the 2010 CODATA recommended values [CODATA2010] 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 codata.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` | 6.64465675e-27 kg
`alpha particle mass energy equivalent` | 5.97191967e-10 J
`alpha particle mass energy equivalent in MeV` | 3727.37924 MeV
`alpha particle mass in u` | 4.00150617913 u
`alpha particle molar mass` | 0.00400150617912 kg mol^-1
`alpha particle-electron mass ratio` | 7294.2995361
`alpha particle-proton mass ratio` | 3.97259968933
`Angstrom star` | 1.00001495e-10 m
`atomic mass constant` | 1.660538921e-27 kg
`atomic mass constant energy equivalent` | 1.492417954e-10 J
`atomic mass constant energy equivalent in MeV` | 931.494061 MeV
`atomic mass unit-electron volt relationship` | 931494061.0 eV
`atomic mass unit-hartree relationship` | 34231776.845 E_h
`atomic mass unit-hertz relationship` | 2.2523427168e+23 Hz
`atomic mass unit-inverse meter relationship` | 7.5130066042e+14 m^-1
`atomic mass unit-joule relationship` | 1.492417954e-10 J
`atomic mass unit-kelvin relationship` | 1.08095408e+13 K
`atomic mass unit-kilogram relationship` | 1.660538921e-27 kg
`atomic unit of 1st hyperpolarizability` | 3.206361449e-53 C^3 m^3 J^-2
`atomic unit of 2nd hyperpolarizability` | 6.23538054e-65 C^4 m^4 J^-3
`atomic unit of action` | 1.054571726e-34 J s
`atomic unit of charge` | 1.602176565e-19 C
`atomic unit of charge density` | 1.081202338e+12 C m^-3
`atomic unit of current` | 0.00662361795 A
`atomic unit of electric dipole mom.` | 8.47835326e-30 C m
`atomic unit of electric field` | 5.14220652e+11 V m^-1
`atomic unit of electric field gradient` | 9.717362e+21 V m^-2
`atomic unit of electric polarizability` | 1.6487772754e-41 C^2 m^2 J^-1
`atomic unit of electric potential` | 27.21138505 V
`atomic unit of electric quadrupole mom.` | 4.486551331e-40 C m^2
`atomic unit of energy` | 4.35974434e-18 J
`atomic unit of force` | 8.23872278e-08 N
`atomic unit of length` | 5.2917721092e-11 m
`atomic unit of mag. dipole mom.` | 1.854801936e-23 J T^-1
`atomic unit of mag. flux density` | 235051.7464 T
`atomic unit of magnetizability` | 7.891036607e-29 J T^-2
`atomic unit of mass` | 9.10938291e-31 kg
`atomic unit of mom.um` | 1.99285174e-24 kg m s^-1
`atomic unit of permittivity` | 1.11265005605e-10 F m^-1
`atomic unit of time` | 2.4188843265e-17 s
`atomic unit of velocity` | 2187691.26379 m s^-1
`Avogadro constant` | 6.02214129e+23 mol^-1
`Bohr magneton` | 9.27400968e-24 J T^-1
`Bohr magneton in eV/T` | 5.7883818066e-05 eV T^-1
`Bohr magneton in Hz/T` | 13996245550.0 Hz T^-1
`Bohr magneton in inverse meters per tesla` | 46.6864498 m^-1 T^-1
`Bohr magneton in K/T` | 0.67171388 K T^-1
`Bohr radius` | 5.2917721092e-11 m
`Boltzmann constant` | 1.3806488e-23 J K^-1
`Boltzmann constant in eV/K` | 8.6173324e-05 eV K^-1
`Boltzmann constant in Hz/K` | 20836618000.0 Hz K^-1
`Boltzmann constant in inverse meters per kelvin` | 69.503476 m^-1 K^-1
`characteristic impedance of vacuum` | 376.730313462 ohm
`classical electron radius` | 2.8179403267e-15 m
`Compton wavelength` | 2.4263102389e-12 m
`Compton wavelength over 2 pi` | 3.86159268e-13 m
`conductance quantum` | 7.7480917346e-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` | 0.8574382308
`deuteron mag. mom.` | 4.33073489e-27 J T^-1
`deuteron mag. mom. to Bohr magneton ratio` | 0.0004669754556
`deuteron mag. mom. to nuclear magneton ratio` | 0.8574382308
`deuteron mass` | 3.34358348e-27 kg
`deuteron mass energy equivalent` | 3.00506297e-10 J
`deuteron mass energy equivalent in MeV` | 1875.612859 MeV
`deuteron mass in u` | 2.01355321271 u
`deuteron molar mass` | 0.00201355321271 kg mol^-1
`deuteron rms charge radius` | 2.1424e-15 m
`deuteron-electron mag. mom. ratio` | -0.0004664345537
`deuteron-electron mass ratio` | 3670.4829652
`deuteron-neutron mag. mom. ratio` | -0.44820652
`deuteron-proton mag. mom. ratio` | 0.307012207
`deuteron-proton mass ratio` | 1.99900750097
`electric constant` | 8.85418781762e-12 F m^-1
`electron charge to mass quotient` | -1.758820088e+11 C kg^-1
`electron g factor` | -2.00231930436
`electron gyromag. ratio` | 1.760859708e+11 s^-1 T^-1
`electron gyromag. ratio over 2 pi` | 28024.95266 MHz T^-1
`electron mag. mom.` | -9.2847643e-24 J T^-1
`electron mag. mom. anomaly` | 0.00115965218076
`electron mag. mom. to Bohr magneton ratio` | -1.00115965218
`electron mag. mom. to nuclear magneton ratio` | -1838.2819709
`electron mass` | 9.10938291e-31 kg
`electron mass energy equivalent` | 8.18710506e-14 J
`electron mass energy equivalent in MeV` | 0.510998928 MeV
`electron mass in u` | 0.00054857990946 u
`electron molar mass` | 5.4857990946e-07 kg mol^-1
`electron to alpha particle mass ratio` | 0.000137093355578
`electron to shielded helion mag. mom. ratio` | 864.058257
`electron to shielded proton mag. mom. ratio` | -658.2275971
`electron volt` | 1.602176565e-19 J
`electron volt-atomic mass unit relationship` | 1.07354415e-09 u
`electron volt-hartree relationship` | 0.03674932379 E_h
`electron volt-hertz relationship` | 2.417989348e+14 Hz
`electron volt-inverse meter relationship` | 806554.429 m^-1
`electron volt-joule relationship` | 1.602176565e-19 J
`electron volt-kelvin relationship` | 11604.519 K
`electron volt-kilogram relationship` | 1.782661845e-36 kg
`electron-deuteron mag. mom. ratio` | -2143.923498
`electron-deuteron mass ratio` | 0.00027244371095
`electron-helion mass ratio` | 0.00018195430761
`electron-muon mag. mom. ratio` | 206.7669896
`electron-muon mass ratio` | 0.00483633166
`electron-neutron mag. mom. ratio` | 960.9205
`electron-neutron mass ratio` | 0.00054386734461
`electron-proton mag. mom. ratio` | -658.2106848
`electron-proton mass ratio` | 0.00054461702178
`electron-tau mass ratio` | 0.000287592
`electron-triton mass ratio` | 0.00018192000653
`elementary charge` | 1.602176565e-19 C
`elementary charge over h` | 2.417989348e+14 A J^-1
`Faraday constant` | 96485.3365 C mol^-1
`Faraday constant for conventional electric current` | 96485.3321 C_90 mol^-1
`Fermi coupling constant` | 1.166364e-05 GeV^-2
`fine-structure constant` | 0.0072973525698
`first radiation constant` | 3.74177153e-16 W m^2
`first radiation constant for spectral radiance` | 1.191042869e-16 W m^2 sr^-1
`Hartree energy` | 4.35974434e-18 J
`Hartree energy in eV` | 27.21138505 eV
`hartree-atomic mass unit relationship` | 2.9212623246e-08 u
`hartree-electron volt relationship` | 27.21138505 eV
`hartree-hertz relationship` | 6.57968392073e+15 Hz
`hartree-inverse meter relationship` | 21947463.1371 m^-1
`hartree-joule relationship` | 4.35974434e-18 J
`hartree-kelvin relationship` | 315775.04 K
`hartree-kilogram relationship` | 4.85086979e-35 kg
`helion g factor` | -4.255250613
`helion mag. mom.` | -1.074617486e-26 J T^-1
`helion mag. mom. to Bohr magneton ratio` | -0.001158740958
`helion mag. mom. to nuclear magneton ratio` | -2.127625306
`helion mass` | 5.00641234e-27 kg
`helion mass energy equivalent` | 4.49953902e-10 J
`helion mass energy equivalent in MeV` | 2808.391482 MeV
`helion mass in u` | 3.0149322468 u
`helion molar mass` | 0.0030149322468 kg mol^-1
`helion-electron mass ratio` | 5495.8852754
`helion-proton mass ratio` | 2.9931526707
`hertz-atomic mass unit relationship` | 4.4398216689e-24 u
`hertz-electron volt relationship` | 4.135667516e-15 eV
`hertz-hartree relationship` | 1.519829846e-16 E_h
`hertz-inverse meter relationship` | 3.33564095198e-09 m^-1
`hertz-joule relationship` | 6.62606957e-34 J
`hertz-kelvin relationship` | 4.7992434e-11 K
`hertz-kilogram relationship` | 7.37249668e-51 kg
`inverse fine-structure constant` | 137.035999074
`inverse meter-atomic mass unit relationship` | 1.3310250512e-15 u
`inverse meter-electron volt relationship` | 1.23984193e-06 eV
`inverse meter-hartree relationship` | 4.55633525276e-08 E_h
`inverse meter-hertz relationship` | 299792458.0 Hz
`inverse meter-joule relationship` | 1.986445684e-25 J
`inverse meter-kelvin relationship` | 0.01438777 K
`inverse meter-kilogram relationship` | 2.210218902e-42 kg
`inverse of conductance quantum` | 12906.4037217 ohm
`Josephson constant` | 4.8359787e+14 Hz V^-1
`joule-atomic mass unit relationship` | 6700535850.0 u
`joule-electron volt relationship` | 6.24150934e+18 eV
`joule-hartree relationship` | 2.29371248e+17 E_h
`joule-hertz relationship` | 1.509190311e+33 Hz
`joule-inverse meter relationship` | 5.03411701e+24 m^-1
`joule-kelvin relationship` | 7.2429716e+22 K
`joule-kilogram relationship` | 1.11265005605e-17 kg
`kelvin-atomic mass unit relationship` | 9.2510868e-14 u
`kelvin-electron volt relationship` | 8.6173324e-05 eV
`kelvin-hartree relationship` | 3.1668114e-06 E_h
`kelvin-hertz relationship` | 20836618000.0 Hz
`kelvin-inverse meter relationship` | 69.503476 m^-1
`kelvin-joule relationship` | 1.3806488e-23 J
`kelvin-kilogram relationship` | 1.536179e-40 kg
`kilogram-atomic mass unit relationship` | 6.02214129e+26 u
`kilogram-electron volt relationship` | 5.60958885e+35 eV
`kilogram-hartree relationship` | 2.061485968e+34 E_h
`kilogram-hertz relationship` | 1.356392608e+50 Hz
`kilogram-inverse meter relationship` | 4.52443873e+41 m^-1
`kilogram-joule relationship` | 8.98755178737e+16 J
`kilogram-kelvin relationship` | 6.5096582e+39 K
`lattice parameter of silicon` | 5.431020504e-10 m
`Loschmidt constant (273.15 K, 100 kPa)` | 2.6516462e+25 m^-3
`Loschmidt constant (273.15 K, 101.325 kPa)` | 2.6867805e+25 m^-3
`mag. constant` | 1.25663706144e-06 N A^-2
`mag. flux quantum` | 2.067833758e-15 Wb
`Mo x unit` | 1.00209952e-13 m
`molar gas constant` | 8.3144621 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` | 3.9903127176e-10 J s mol^-1
`molar Planck constant times c` | 0.119626565779 J m mol^-1
`molar volume of ideal gas (273.15 K, 100 kPa)` | 0.022710953 m^3 mol^-1
`molar volume of ideal gas (273.15 K, 101.325 kPa)` | 0.022413968 m^3 mol^-1
`molar volume of silicon` | 1.205883301e-05 m^3 mol^-1
`muon Compton wavelength` | 1.173444103e-14 m
`muon Compton wavelength over 2 pi` | 1.867594294e-15 m
`muon g factor` | -2.0023318418
`muon mag. mom.` | -4.49044807e-26 J T^-1
`muon mag. mom. anomaly` | 0.00116592091
`muon mag. mom. to Bohr magneton ratio` | -0.00484197044
`muon mag. mom. to nuclear magneton ratio` | -8.89059697
`muon mass` | 1.883531475e-28 kg
`muon mass energy equivalent` | 1.692833667e-11 J
`muon mass energy equivalent in MeV` | 105.6583715 MeV
`muon mass in u` | 0.1134289267 u
`muon molar mass` | 0.0001134289267 kg mol^-1
`muon-electron mass ratio` | 206.7682843
`muon-neutron mass ratio` | 0.1124545177
`muon-proton mag. mom. ratio` | -3.183345107
`muon-proton mass ratio` | 0.1126095272
`muon-tau mass ratio` | 0.0594649
`natural unit of action` | 1.054571726e-34 J s
`natural unit of action in eV s` | 6.58211928e-16 eV s
`natural unit of energy` | 8.18710506e-14 J
`natural unit of energy in MeV` | 0.510998928 MeV
`natural unit of length` | 3.86159268e-13 m
`natural unit of mass` | 9.10938291e-31 kg
`natural unit of mom.um` | 2.73092429e-22 kg m s^-1
`natural unit of mom.um in MeV/c` | 0.510998928 MeV/c
`natural unit of time` | 1.28808866833e-21 s
`natural unit of velocity` | 299792458.0 m s^-1
`neutron Compton wavelength` | 1.3195909068e-15 m
`neutron Compton wavelength over 2 pi` | 2.1001941568e-16 m
`neutron g factor` | -3.82608545
`neutron gyromag. ratio` | 183247179.0 s^-1 T^-1
`neutron gyromag. ratio over 2 pi` | 29.1646943 MHz T^-1
`neutron mag. mom.` | -9.6623647e-27 J T^-1
`neutron mag. mom. to Bohr magneton ratio` | -0.00104187563
`neutron mag. mom. to nuclear magneton ratio` | -1.91304272
`neutron mass` | 1.674927351e-27 kg
`neutron mass energy equivalent` | 1.505349631e-10 J
`neutron mass energy equivalent in MeV` | 939.565379 MeV
`neutron mass in u` | 1.008664916 u
`neutron molar mass` | 0.001008664916 kg mol^-1
`neutron to shielded proton mag. mom. ratio` | -0.68499694
`neutron-electron mag. mom. ratio` | 0.00104066882
`neutron-electron mass ratio` | 1838.6836605
`neutron-muon mass ratio` | 8.892484
`neutron-proton mag. mom. ratio` | -0.68497934
`neutron-proton mass difference` | 2.30557392e-30
`neutron-proton mass difference energy equivalent` | 2.0721465e-13
`neutron-proton mass difference energy equivalent in MeV` | 1.29333217
`neutron-proton mass difference in u` | 0.00138844919
`neutron-proton mass ratio` | 1.00137841917
`neutron-tau mass ratio` | 0.52879
`Newtonian constant of gravitation` | 6.67384e-11 m^3 kg^-1 s^-2
`Newtonian constant of gravitation over h-bar c` | 6.70837e-39 (GeV/c^2)^-2
`nuclear magneton` | 5.05078353e-27 J T^-1
`nuclear magneton in eV/T` | 3.1524512605e-08 eV T^-1
`nuclear magneton in inverse meters per tesla` | 0.02542623527 m^-1 T^-1
`nuclear magneton in K/T` | 0.00036582682 K T^-1
`nuclear magneton in MHz/T` | 7.62259357 MHz T^-1
`Planck constant` | 6.62606957e-34 J s
`Planck constant in eV s` | 4.135667516e-15 eV s
`Planck constant over 2 pi` | 1.054571726e-34 J s
`Planck constant over 2 pi in eV s` | 6.58211928e-16 eV s
`Planck constant over 2 pi times c in MeV fm` | 197.3269718 MeV fm
`Planck length` | 1.616199e-35 m
`Planck mass` | 2.17651e-08 kg
`Planck mass energy equivalent in GeV` | 1.220932e+19 GeV
`Planck temperature` | 1.416833e+32 K
`Planck time` | 5.39106e-44 s
`proton charge to mass quotient` | 95788335.8 C kg^-1
`proton Compton wavelength` | 1.32140985623e-15 m
`proton Compton wavelength over 2 pi` | 2.1030891047e-16 m
`proton g factor` | 5.585694713
`proton gyromag. ratio` | 267522200.5 s^-1 T^-1
`proton gyromag. ratio over 2 pi` | 42.5774806 MHz T^-1
`proton mag. mom.` | 1.410606743e-26 J T^-1
`proton mag. mom. to Bohr magneton ratio` | 0.00152103221
`proton mag. mom. to nuclear magneton ratio` | 2.792847356
`proton mag. shielding correction` | 2.5694e-05
`proton mass` | 1.672621777e-27 kg
`proton mass energy equivalent` | 1.503277484e-10 J
`proton mass energy equivalent in MeV` | 938.272046 MeV
`proton mass in u` | 1.00727646681 u
`proton molar mass` | 0.00100727646681 kg mol^-1
`proton rms charge radius` | 8.775e-16 m
`proton-electron mass ratio` | 1836.15267245
`proton-muon mass ratio` | 8.88024331
`proton-neutron mag. mom. ratio` | -1.45989806
`proton-neutron mass ratio` | 0.99862347826
`proton-tau mass ratio` | 0.528063
`quantum of circulation` | 0.0003636947552 m^2 s^-1
`quantum of circulation times 2` | 0.0007273895104 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` | 13.60569253 eV
`Rydberg constant times hc in J` | 2.179872171e-18 J
`Sackur-Tetrode constant (1 K, 100 kPa)` | -1.1517078
`Sackur-Tetrode constant (1 K, 101.325 kPa)` | -1.1648708
`second radiation constant` | 0.01438777 m K
`shielded helion gyromag. ratio` | 203789465.9 s^-1 T^-1
`shielded helion gyromag. ratio over 2 pi` | 32.43410084 MHz T^-1
`shielded helion mag. mom.` | -1.074553044e-26 J T^-1
`shielded helion mag. mom. to Bohr magneton ratio` | -0.001158671471
`shielded helion mag. mom. to nuclear magneton ratio` | -2.127497718
`shielded helion to proton mag. mom. ratio` | -0.761766558
`shielded helion to shielded proton mag. mom. ratio` | -0.7617861313
`shielded proton gyromag. ratio` | 267515326.8 s^-1 T^-1
`shielded proton gyromag. ratio over 2 pi` | 42.5763866 MHz T^-1
`shielded proton mag. mom.` | 1.410570499e-26 J T^-1
`shielded proton mag. mom. to Bohr magneton ratio` | 0.001520993128
`shielded proton mag. mom. to nuclear magneton ratio` | 2.792775598
`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` | 5.670373e-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` | 6.652458734e-29 m^2
`triton g factor` | 5.957924896
`triton mag. mom.` | 1.504609447e-26 J T^-1
`triton mag. mom. to Bohr magneton ratio` | 0.001622393657
`triton mag. mom. to nuclear magneton ratio` | 2.978962448
`triton mass` | 5.0073563e-27 kg
`triton mass energy equivalent` | 4.50038741e-10 J
`triton mass energy equivalent in MeV` | 2808.921005 MeV
`triton mass in u` | 3.0155007134 u
`triton molar mass` | 0.0030155007134 kg mol^-1
`triton-electron mass ratio` | 5496.9215267
`triton-proton mass ratio` | 2.9937170308
`unified atomic mass unit` | 1.660538921e-27 kg
`von Klitzing constant` | 25812.8074434 ohm
`weak mixing angle` | 0.2223
`Wien frequency displacement law constant` | 58789254000.0 Hz K^-1
`Wien wavelength displacement law constant` | 0.0028977721 m K
`{220} lattice spacing of silicon` | 1.920155714e-10 m

## Units

### SI prefixes

`yotta` |
`zetta` |
`exa` |
`peta` |
`tera` |
`giga` |
`mega` |
`kilo` |
`hecto` |
`deka` |
`deci` |
`centi` |
`milli` |
`micro` |
`nano` |
`pico` |
`femto` |
`atto` |
`zepto` |

### Binary prefixes

`kibi` |
`mebi` |
`gibi` |
`tebi` |
`pebi` |
`exbi` |
`zebi` |
`yobi` |

### Weight

`gram` | kg
`metric_ton` | kg
`grain` | one grain in kg
`lb` | one pound (avoirdupous) in kg
`oz` | 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)

### Angle

`degree` | degree in radians
`arcmin` | arc minute in radians
`arcsec` | 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
`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
`light_year` | one light year in meters
`parsec` | one parsec in meters

### Pressure

`atm` | standard atmosphere in pascals
`bar` | one bar in pascals
`torr` | 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
`gallon` | 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_imp` | one fluid ounce (UK) in cubic meters
`bbl` | 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
`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
`calorie` | 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_th` | one British thermal unit (thermochemical) in Joules
`ton_TNT` | one ton of TNT in Joules

### Power

`hp` | one horsepower in watts

### Force

`dyn` | one dyne in newtons
`lbf` | one pound force in newtons
`kgf` | one kilogram force in newtons

### Optics

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

## References

[CODATA2010] | CODATA Recommended Values of the Fundamental Physical Constants 2010. http://physics.nist.gov/cuu/Constants/index.html

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