  The effects of thermal fluctuations of the mass (horizon area) and electric
charge, on the entropy of non-rotating charged {\it macroscopic} black holes,
are analyzed using a grand canonical ensemble. Restricting to Gaussian
fluctuations around equilibrium, and assuming a power law type of relation
between the black hole mass, charge and horizon area, characterized by two real
positive indices, the grand canonical entropy is shown to acquire a logarithmic
correction with a positive coefficient proportional to the sum of the indices.
However, the root mean squared fluctuations of mass and charge relative to the
mean values of these quantities turn out to be independent of the details of
the assumed mass-area relation. We also comment on possible cancellation
between log (area) corrections arising due to {\it fixed area} quantum
spacetime fluctuations and that due to thermal fluctuations of the area and
other quantities.
