The electrical capacitance of several small systems is determined by using results given by the fluctuation-dissipation theorem in the classical limit. Estimating the electrical capacitance is important because it is the link to knowledge of the fluctuation of several physical quantities, voltage and field fluctuations, dipole moment, pH, and charge, and also to knowledge of the polarizability and the dielectric dispersion of colloidal and polyelectrolyte systems. For small systems appearing in nature similar to(10-1000) Angstrom the electric capacitance varies in the range similar to(10-1000) x 10(-18) F with the corresponding field and dipole moment fluctuations in the order of units of (10(4) - 10(6)) V/m and (10(2) - 10(4)) D, respectively.