### Navigation

- index
- modules |
- next |
- previous |
- SciPy v0.7 Reference Guide (DRAFT) »

# 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 containing physical constants, `scipy.constants` also contains a database of additional physical constants.

`value` (key) | value indexed by key
`unit` (key) | unit indexed by key
`precision` (key) | relative precision indexed by key
`find` (sub) | list all keys containing the string sub

`scipy.constants.``physical_constants`

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

  Available constants:

  `alpha particle mass` |
  `alpha particle mass energy equivalent` |
  `alpha particle mass energy equivalent in MeV` |
  `alpha particle mass in u` |
  `alpha particle molar mass` |
  `alpha particle-electron mass ratio` |
  `alpha particle-proton mass ratio` |
  `Angstrom star` |
  `atomic mass constant` |
  `atomic mass constant energy equivalent` |
  `atomic mass constant energy equivalent in MeV` |
  `atomic mass unit-electron volt relationship` |
  `atomic mass unit-hartree relationship` |
  `atomic mass unit-hertz relationship` |
  `atomic mass unit-inverse meter relationship` |
  `atomic mass unit-joule relationship` |
  `atomic mass unit-kelvin relationship` |
  `atomic mass unit-kilogram relationship` |
  `atomic unit of 1st hyperpolarizablity` |
  `atomic unit of 2nd hyperpolarizablity` |
  `atomic unit of action` |
  `atomic unit of charge` |
  `atomic unit of charge density` |
  `atomic unit of current` |
  `atomic unit of electric dipole moment` |
  `atomic unit of electric field` |
  `atomic unit of electric field gradient` |
  `atomic unit of electric polarizablity` |
  `atomic unit of electric potential` |
  `atomic unit of electric quadrupole moment` |
  `atomic unit of energy` |
  `atomic unit of force` |
  `atomic unit of length` |
  `atomic unit of magnetic dipole moment` |
  `atomic unit of magnetic flux density` |
  `atomic unit of magnetizability` |
  `atomic unit of mass` |
  `atomic unit of momentum` |
  `atomic unit of permittivity` |
  `atomic unit of time` |
  `atomic unit of velocity` |
  `Avogadro constant` |
  `Bohr magneton` |
  `Bohr magneton in eV/T` |
  `Bohr magneton in Hz/T` |
  `Bohr magneton in inverse meters per tesla` |
  `Bohr magneton in K/T` |
  `Bohr radius` |
  `Boltzmann constant` |
  `Boltzmann constant in eV/K` |
  `Boltzmann constant in Hz/K` |
  `Boltzmann constant in inverse meters per kelvin` |
  `characteristic impedance of vacuum` |
  `classical electron radius` |
  `Compton wavelength` |
  `Compton wavelength over 2 pi` |
  `conductance quantum` |
  `conventional value of Josephson constant` |
  `conventional value of von Klitzing constant` |
  `Cu x unit` |
  `deuteron magnetic moment` |
  `deuteron magnetic moment to Bohr magneton ratio` |
  `deuteron magnetic moment to nuclear magneton ratio` |
  `deuteron mass` |
  `deuteron mass energy equivalent` |
  `deuteron mass energy equivalent in MeV` |
  `deuteron mass in u` |
  `deuteron molar mass` |
  `deuteron rms charge radius` |
  `deuteron-electron magnetic moment ratio` |
  `deuteron-electron mass ratio` |
  `deuteron-neutron magnetic moment ratio` |
  `deuteron-proton magnetic moment ratio` |
  `deuteron-proton mass ratio` |
  `electric constant` |
  `electron charge to mass quotient` |
  `electron g factor` |
  `electron gyromagnetic ratio` |
  `electron gyromagnetic ratio over 2 pi` |
  `electron magnetic moment` |
  `electron magnetic moment anomaly` |
  `electron magnetic moment to Bohr magneton ratio` |
  `electron magnetic moment to nuclear magneton ratio` |
  `electron mass` |
  `electron mass energy equivalent` |
  `electron mass energy equivalent in MeV` |
  `electron mass in u` |
  `electron molar mass` |
  `electron to alpha particle mass ratio` |
  `electron to shielded helion magnetic moment ratio` |
  `electron to shielded proton magnetic moment ratio` |
  `electron volt` |
  `electron volt-atomic mass unit relationship` |
  `electron volt-hartree relationship` |
  `electron volt-hertz relationship` |
  `electron volt-inverse meter relationship` |
  `electron volt-joule relationship` |
  `electron volt-kelvin relationship` |
  `electron volt-kilogram relationship` |
  `electron-deuteron magnetic moment ratio` |
  `electron-deuteron mass ratio` |
  `electron-muon magnetic moment ratio` |
  `electron-muon mass ratio` |
  `electron-neutron magnetic moment ratio` |
  `electron-neutron mass ratio` |
  `electron-proton magnetic moment ratio` |
  `electron-proton mass ratio` |
  `electron-tau mass ratio` |
  `elementary charge` |
  `elementary charge over h` |
  `Faraday constant` |
  `Faraday constant for conventional electric current` |
  `Fermi coupling constant` |
  `fine-structure constant` |
  `first radiation constant` |
  `first radiation constant for spectral radiance` |
  `Hartree energy` |
  `Hartree energy in eV` |
  `hartree-atomic mass unit relationship` |
  `hartree-electron volt relationship` |
  `hartree-hertz relationship` |
  `hartree-inverse meter relationship` |
  `hartree-joule relationship` |
  `hartree-kelvin relationship` |
  `hartree-kilogram relationship` |
  `helion mass` |
  `helion mass energy equivalent` |
  `helion mass energy equivalent in MeV` |
  `helion mass in u` |
  `helion molar mass` |
  `helion-electron mass ratio` |
  `helion-proton mass ratio` |
  `hertz-atomic mass unit relationship` |
  `hertz-electron volt relationship` |
  `hertz-hartree relationship` |
  `hertz-inverse meter relationship` |
  `hertz-joule relationship` |
  `hertz-kelvin relationship` |
  `hertz-kilogram relationship` |
  `inverse fine-structure constant` |
  `inverse meter-atomic mass unit relationship` |
  `inverse meter-electron volt relationship` |
  `inverse meter-hartree relationship` |
  `inverse meter-hertz relationship` |
  `inverse meter-joule relationship` |
  `inverse meter-kelvin relationship` |
  `inverse meter-kilogram relationship` |
  `inverse of conductance quantum` |
  `Josephson constant` |
  `joule-atomic mass unit relationship` |
  `joule-electron volt relationship` |
  `joule-hartree relationship` |
  `joule-hertz relationship` |
  `joule-inverse meter relationship` |
  `joule-kelvin relationship` |
  `joule-kilogram relationship` |
  `kelvin-atomic mass unit relationship` |
  `kelvin-electron volt relationship` |
  `kelvin-hartree relationship` |
  `kelvin-hertz relationship` |
  `kelvin-inverse meter relationship` |
  `kelvin-joule relationship` |
  `kelvin-kilogram relationship` |
  `kilogram-atomic mass unit relationship` |
  `kilogram-electron volt relationship` |
  `kilogram-hartree relationship` |
  `kilogram-hertz relationship` |
  `kilogram-inverse meter relationship` |
  `kilogram-joule relationship` |
  `kilogram-kelvin relationship` |
  `lattice parameter of silicon` |
  `Loschmidt constant (273.15 K, 101.325 kPa)` |
  `magnetic constant` |
  `magnetic flux quantum` |
  `Mo x unit` |
  `molar gas constant` |
  `molar mass constant` |
  `molar mass of carbon-12` |
  `molar Planck constant` |
  `molar Planck constant times c` |
  `molar volume of ideal gas (273.15 K, 100 kPa)` |
  `molar volume of ideal gas (273.15 K, 101.325 kPa)` |
  `molar volume of silicon` |
  `muon Compton wavelength` |
  `muon Compton wavelength over 2 pi` |
  `muon g factor` |
  `muon magnetic moment` |
  `muon magnetic moment anomaly` |
  `muon magnetic moment to Bohr magneton ratio` |
  `muon magnetic moment to nuclear magneton ratio` |
  `muon mass` |
  `muon mass energy equivalent` |
  `muon mass energy equivalent in MeV` |
  `muon mass in u` |
  `muon molar mass` |
  `muon-electron mass ratio` |
  `muon-neutron mass ratio` |
  `muon-proton magnetic moment ratio` |
  `muon-proton mass ratio` |
  `muon-tau mass ratio` |
  `natural unit of action` |
  `natural unit of action in eV s` |
  `natural unit of energy` |
  `natural unit of energy in MeV` |
  `natural unit of length` |
  `natural unit of mass` |
  `natural unit of momentum` |
  `natural unit of momentum in MeV/c` |
  `natural unit of time` |
  `natural unit of velocity` |
  `neutron Compton wavelength` |
  `neutron Compton wavelength over 2 pi` |
  `neutron g factor` |
  `neutron gyromagnetic ratio` |
  `neutron gyromagnetic ratio over 2 pi` |
  `neutron magnetic moment` |
  `neutron magnetic moment to Bohr magneton ratio` |
  `neutron magnetic moment to nuclear magneton ratio` |
  `neutron mass` |
  `neutron mass energy equivalent` |
  `neutron mass energy equivalent in MeV` |
  `neutron mass in u` |
  `neutron molar mass` |
  `neutron to shielded proton magnetic moment ratio` |
  `neutron-electron magnetic moment ratio` |
  `neutron-electron mass ratio` |
  `neutron-muon mass ratio` |
  `neutron-proton magnetic moment ratio` |
  `neutron-proton mass ratio` |
  `neutron-tau mass ratio` |
  `Newtonian constant of gravitation` |
  `Newtonian constant of gravitation over h-bar c` |
  `nuclear magneton` |
  `nuclear magneton in eV/T` |
  `nuclear magneton in inverse meters per tesla` |
  `nuclear magneton in K/T` |
  `nuclear magneton in MHz/T` |
  `Planck constant` |
  `Planck constant in eV s` |
  `Planck constant over 2 pi` |
  `Planck constant over 2 pi in eV s` |
  `Planck constant over 2 pi times c in MeV fm` |
  `Planck length` |
  `Planck mass` |
  `Planck temperature` |
  `Planck time` |
  `proton charge to mass quotient` |
  `proton Compton wavelength` |
  `proton Compton wavelength over 2 pi` |
  `proton g factor` |
  `proton gyromagnetic ratio` |
  `proton gyromagnetic ratio over 2 pi` |
  `proton magnetic moment` |
  `proton magnetic moment to Bohr magneton ratio` |
  `proton magnetic moment to nuclear magneton ratio` |
  `proton magnetic shielding correction` |
  `proton mass` |
  `proton mass energy equivalent` |
  `proton mass energy equivalent in MeV` |
  `proton mass in u` |
  `proton molar mass` |
  `proton rms charge radius` |
  `proton-electron mass ratio` |
  `proton-muon mass ratio` |
  `proton-neutron magnetic moment ratio` |
  `proton-neutron mass ratio` |
  `proton-tau mass ratio` |
  `quantum of circulation` |
  `quantum of circulation times 2` |
  `Rydberg constant` |
  `Rydberg constant times c in Hz` |
  `Rydberg constant times hc in eV` |
  `Rydberg constant times hc in J` |
  `Sackur-Tetrode constant (1 K, 100 kPa)` |
  `Sackur-Tetrode constant (1 K, 101.325 kPa)` |
  `second radiation constant` |
  `shielded helion gyromagnetic ratio` |
  `shielded helion gyromagnetic ratio over 2 pi` |
  `shielded helion magnetic moment` |
  `shielded helion magnetic moment to Bohr magneton ratio` |
  `shielded helion magnetic moment to nuclear magneton ratio` |
  `shielded helion to proton magnetic moment ratio` |
  `shielded helion to shielded proton magnetic moment ratio` |
  `shielded proton gyromagnetic ratio` |
  `shielded proton gyromagnetic ratio over 2 pi` |
  `shielded proton magnetic moment` |
  `shielded proton magnetic moment to Bohr magneton ratio` |
  `shielded proton magnetic moment to nuclear magneton ratio` |
  `speed of light in vacuum` |
  `standard acceleration of gravity` |
  `standard atmosphere` |
  `Stefan-Boltzmann constant` |
  `tau Compton wavelength` |
  `tau Compton wavelength over 2 pi` |
  `tau mass` |
  `tau mass energy equivalent` |
  `tau mass energy equivalent in MeV` |
  `tau mass in u` |
  `tau molar mass` |
  `tau-electron mass ratio` |
  `tau-muon mass ratio` |
  `tau-neutron mass ratio` |
  `tau-proton mass ratio` |
  `Thomson cross section` |
  `unified atomic mass unit` |
  `von Klitzing constant` |
  `weak mixing angle` |
  `Wien displacement law constant` |
  `{220} lattice spacing of silicon` |

## Unit prefixes

### SI

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

### Binary

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

## Units

### 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 Ångström 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 Celcius to Kelvin
`K2C` (K) | Convert Kelvin to Celcius
`F2C` (F) | Convert Fahrenheit to Celcius
`C2F` (C) | Convert Celcius 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 watts
`lbf` | one pound force in watts
`kgf` | one kilogram force in watts

### Optics

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

### Navigation

- index
- modules |
- next |
- previous |
- SciPy v0.7 Reference Guide (DRAFT) »