### Theory:

The property of a material that helps the movement of charges and thus the current flow in the circuit is known as conductance. It is denoted as $$G$$.
Mathematically, it is defined as the reciprocal of its resistance ($$R$$).

The formula of conductance '$$G$$' is given by

The SI unit of conductance of a material is $$ohm^{–1}$$ (or) $$mho$$ (or) $$siemen$$.

Conductivity:
Electrical conductivity is the reciprocal of the electrical resistivity of a material. The SI unit is $$ohm^{–1}\ metre^{–1}$$ (or) $$mho\ metre^{–1}$$ (or) $$siemen\ metre^{–1}$$.
The formula of conductivity is given by

$\mathrm{\sigma } =\phantom{\rule{0.147em}{0ex}}\frac{1}{\mathrm{\rho }}$
Electrical conductivity is a measure of a material's ability to pass the current through it.
The conductivity of conductors is higher than that of insulators. However, the resistivity of conductors is lesser than that of insulators.

Like resistivity, conductivity is also constant for a material. Resistivity of some common materials are shown in the table below.

 Material's nature Material Resistivity of material ($$\Omega\ m$$) Conductor Copper Nickel Chromium $$1.62\times{10^{-8}}$$ $$6.84\times{10^{-8}}$$ $$12.9\times{10^{-8}}$$ Insulator Glass Rubber $$10^{10}$$ to $$10^{14}$$ $$10^{13}$$ to $$10^{16}$$