Gauss’s law states that the electric flux through a closed surface is a measure of the charge within it.
Where $\vec E$ is the electric field, S is some closed surface, $d\vec A$ is an infinitesimal surface area whose vector points normal to S, Q is the enclosed charge, and $\epsilon_0$ is the permittivity of free space, the integral form of Gauss’s law can be written as $$ \oint_S \vec E \cdot \mathrm d\vec A = \frac{1}{\epsilon_0}Q $$
Old math.