The macroscopic Beckenstain-Hawking entropy formula

$$ S_{BH} = \frac{k A}{4 l_p^2} $$

with the Planck length given by

$$ l_p = \sqrt{\frac{G\hbar}{c^3}} $$

gives a hint that quantum gravity is needed to determine the entropy because it contains both, the gravity constant $G$ and Plancks constant $\hbar$.

However, this formula does NOT say what the correct quantum gravity is, that is needed to correctly describe the microstates of the black hole. Assuming a certain quantum gravity and calculating the entropy from a statistical mechanics point of view by counting the microstates

$$ S = -k \sum\limits_i P_i \ln P_i $$

where $P_i$ is the probability that the system is in the microstate $i$, the Beckenstein-Hawking formula must be reproducable.

If it does not, the quantum gravity applied is wrong.

In summary, the Beckenstein-Hawking formula is not a quantum gravity theory, but it can be used as a test of all wannabe quantum gravities.