Fundamental Constants

The fixed numbers the universe runs on. Values below follow the SI definitions; never guess a constant — look it up.

Astronomical unit (in metres) (au)

149597870700 m

Atomic mass unit (u)

1.66053906660e-27 kg

Avogadro constant (N_A)

6.02214076e23 /mol

Bohr radius (a₀)

5.29177210903e-11 m

Boltzmann constant (k)

1.380649e-23 J/K

Earth mass (M⊕)

5.97237e24 kg

Earth radius (mean) (R⊕)

6371000 m

Electron mass (m_e)

9.1093837015e-31 kg

Elementary charge (e)

1.602176634e-19 C

Fine-structure constant (α)

7.2973525693e-3 dimensionless

Gravitational constant (G)

6.67430e-11 m³/kg/s²

Hubble constant (H₀)

~70 (km/s)/Mpc

Ideal gas constant (R)

8.314462618 J/(mol·K)

Neutron mass (m_n)

1.67492749804e-27 kg

Planck constant (h)

6.62607015e-34 J·s

Proton charge (+e)

1.602176634e-19 C

Proton mass (m_p)

1.67262192369e-27 kg

Reduced Planck constant (ħ)

1.054571817e-34 J·s

Rydberg constant (R∞)

10973731.568160 m⁻¹

Speed of light in vacuum (c)

299792458 m/s

Standard gravity (g)

9.80665 m/s²

Stefan–Boltzmann constant (σ)

5.670374419e-8 W/(m²·K⁴)

Vacuum permeability (μ₀)

1.25663706212e-6 N/A²

Vacuum permittivity (ε₀)

8.8541878128e-12 F/m