The permittivity of free space or vacuum permittivity, represented by ε0, is a constant representing the relationship between electric charge and force. It is equal to

$ \epsilon_0 = \frac {1}{\mu_0 \ c^2} = 8.854 \ 187 \ 817 \times 10^{-12} \ F/m $ (farads per metre)

where µ0 is the permeability of free space. It is most commonly seen in Coulomb's law and Maxwell's equations.