Non-SI units and some important physical constantsΒΆ


The physical constants are implemented under names derived from their descriptions by replacing spaces with underscores. Additionally, they also have short names, these are:

  • atomic mass unit : amu
  • astronomical unit : AU
  • Boltzmann constant : k, k_B
  • constant of gravitation : G
  • electric constant : epsilon_0
  • electron mass : m_e
  • elementary charge : e_
  • magnetic ocnstant : mu_0
  • mass of jupiter : m_J
  • mass of sun : m_0
  • Planck constant : h_
  • reduced Planck constant : h_bar
  • Planck length : l_P
  • Planck mass : m_P
  • Planck temperature : T_P
  • Planck time : t_P
  • speed of light : c
  • standard gravity : g_n
  • standard atmosphere : atm

Note the trailing underscores on the elementary charge and on the Planck constant. These are to avoid confusion with the mathematical constant e and the symbol for hour, h, respectively. Keep in mind that some short names can easily be overwritten by accident (e.g. c).

Some other units whose implementation names may be unintuitive are

  • nautical mile : nmile
  • imperial gallon : impGal (also: gallon)
  • US gallon : usGal
  • imperial fluid ounce : impFlOz
  • US fluid ounce : usFlOz

For a list of all pre-defined units see Quantity.all_unit_names at runtime.

Additionally, the SI prefixes are implemented as numbers using their long names:

yotta, zetta, exa, peta, tera, giga, mega, kilo, hecto, deca, deci, centi, milli, micro, nano, pico, femto, atto, zepto, yocto

Most of the values for units and constants are from NIST, see


  • David Bate (2008): initial version
  • Miriam Backens (2009): added some more constants


sage: from sage.dimpy import *
sage: AU == astronomical_unit
sage: k
1.3806504e-23 m^2 kg s^-2 K^-1
sage: usGal
sage: c**2 * (mu_0 * epsilon_0)
sage: barn * mega*parsec
0.0030857 l