# 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)

### 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