${\displaystyle F=\frac{1}{4\pi {\epsilon }_0}\cdot \frac{\left|Q_1{Q}_2\right|}{r^2}}$

based on Coulomb's law in a vacuum, where F is the magnitude of the force between two particles with electric charges Q₁ and Q₂ respectively, placed at a distance r apart

Note 1 to entry: In a vacuum, the product of the electric constant ε₀ and the electric field strength E is equal to the electric flux density D:

D = ε₀E

Note 2 to entry: The electric constant ε₀ is related to the magnetic constant μ₀ and to the speed of light in vacuum c₀ by the relation ε₀μ₀c₀² = 1.

Note 3 to entry: The value of the electric constant ε₀ is equal to

$\mathrm{8,854}1878128(13)\cdot {10}^{-12}\frac{\text{A}\cdot \text{s}}{\text{V}\cdot \text{m}}$