Flux is a mathematical concept which can be interpreted physically. In case of an arbitrary surface, electric field is calculated by dividing imaginary surface into small elements of surface. Each element of surface is considered as a flat surface and is represented by a vector. The magnitude of this vector is equal to the area of surface element and direction is along the normal to the surface. If the surface is a closed one, then such vector is to be coming out of the close surface.

Suppose a vector ∆*a*_{n} is an area vector of n^{th} element and the electric field at that element is *E*_{n} then,

*E*_{n} ∆*a*_{n} = electric flux

Electric flux is a scalar product and has a definite number. The unit of electric flux is Nm^{2}/C or Vm.