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Constants

Constants: 36 values with number and unit, taken from our formula anatomy and the SI definitions.  All concepts →

Defining the SI · 5

boltzmann constant 1.380649e-23 joule per kelvin 10
Physical constant relating temperature to energy, appearing in entropy expressions.
speed of light 299792458 metre per second 10
The speed of light in vacuum is a universal constant, approximately 299,792,458 meters per second.
elementary charge 1.602176634e-19 coulomb 9
Magnitude of the electric charge of a single electron or proton
planck constant 6.62607015e-34 joule second 7
Fundamental physical constant that sets the scale of quantum mechanical quantization.
avogadro constant 6.02214076e23 per mole 5
Number of constituent particles per mole

Electromagnetism · 8

bohr magneton 9.2740100783e-24 joule per tesla 48
Bohr magneton, the natural unit of electron magnetic moment.
coulomb constant 8.9875517923e9 newton metre squared per coulomb squared 21
Electrostatic force constant in Coulomb's law
magnetic flux quantum 2.067833848e-15 weber 19
Superconducting flux quantum, h/(2e), the fundamental unit of magnetic flux in a superconductor
von klitzing constant 25812.80745 ohm 18
Von Klitzing constant h/e² — the resistance plateau of the quantum Hall effect, now the resistance standard.
faraday constant 96485.33212 coulomb per mole 17
Charge of one mole of electrons.
vacuum permittivity 8.8541878128e-12 farad per metre 14
Permittivity of free space, a fundamental constant
conductance quantum 7.748091729e-5 siemens 12
Conductance quantum 2e²/h — the step by which conductance changes in a quantum point contact.
vacuum permeability 1.25663706212e-6 henry per metre 7
Magnetic constant of vacuum, linking current to magnetic field.

Particles and the atom · 9

neutron mass 1.67492749804e-27 kilogram 61
Rest mass of the neutron.
proton mass 1.67262192369e-27 kilogram 45
Rest mass of the proton.
electron charge 24
The fundamental unit of electric charge carried by a single electron.
bohr radius 5.29177210903e-11 metre 17
Bohr radius, the natural length scale of the hydrogen atom.
electron mass 9.1093837015e-31 kilogram 13
Rest mass of an electron, a fundamental physical constant.
classical electron radius 2.8179403262e-15 metre 10
Radius of a classical electron
rydberg constant 10973731.568160 per metre 9
Rydberg constant — sets the wavelengths of hydrogen spectral lines; the most precisely measured constant in physics.
atomic mass constant 1.66053906660e-27 kilogram 8
One twelfth of the mass of a carbon-12 atom.
fine structure constant 7.2973525693e-3 4
Fine-structure constant, about 1/137 — the strength of the electromagnetic interaction, a pure number.

Heat and radiation · 3

gas constant 8.314462618 joule per mole kelvin 16
Universal gas constant relating energy scale to temperature
stefan boltzmann constant 5.670374419e-8 watt per square metre kelvin to the fourth 11
stefan boltzmann constant — from formula anatomy
wien displacement constant 2.897771955e-3 metre kelvin 8
Wien's displacement constant, relating peak wavelength to temperature

Gravity and Planck scale · 6

gravitational constant 6.67430e-11 newton metre squared per kilogram squared 45
The physical constant G that appears in Newton's law of universal gravitation and Einstein's field equations.
hubble constant 2.2e-18 per second 39
The Hubble constant measures the rate of expansion of the universe.
planck time 5.391247e-44 second 36
Planck time, light crossing one Planck length.
planck mass 2.176434e-8 kilogram 24
Planck mass, the fundamental mass scale in quantum gravity
planck length 1.616255e-35 metre 16
Planck length, the scale at which spacetime itself is expected to need a quantum description.
reduced planck constant 1.054571817e-34 joule second
The fundamental constant ħ, equal to the Planck constant divided by 2π, central to quantum mechanics.

From our formulas · 5

coupling constant 17
A parameter that quantifies the strength of an interaction between particles or fields.
airy disk constant 1.22 16
First zero of the Airy disk for a circular aperture
imaginary unit 1 11
imaginary unit — from formula anatomy
angular frequency 10
angular frequency — from formula anatomy
pi 3.14159 7
The mathematical constant approximately equal to 3.14159, the ratio of a circle's circumference to its diameter.