If you mean Coulomb's Law, then it's that the magnitude of the force of attraction or repulsion between two charged particles of charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$ is given by the following formula. $F = \frac{1}{4\pi \epsilon_0} \frac{q_1 q_2}{r^2}$Here, $$\epsilon_0$$ is a fundamental constant called the permittivity of free space.