  The metastable states of a glass are counted by adding a weak pinning field
which explicitly breaks the ergodicity. Their entropy, that is the logarithm of
their number, is extensive in a range of temperatures $T_G < T < T_C$ only,
where $T_G$ and $T_C$ correspond to the ideal calorimetric and kinetic glass
transition temperatures respectively. An explicit self-consistent computation
of the metastable states entropy for a non disordered model is given.
