  The Bekenstein-Hawking entropy of black holes in Einstein's theory of gravity
is equal to a quarter of the horizon area in units of Newton's constant. Wald
has proposed that in general theories of gravity the entropy of stationary
black holes with bifurcate Killing horizons is a Noether charge which is in
general different from the Bekenstein-Hawking entropy. We show that the Noether
charge entropy is equal to a quarter of the horizon area in units of the
effective gravitational coupling on the horizon defined by the coefficient of
the kinetic term of specific graviton polarizations on the horizon. We present
several explicit examples of static spherically symmetric black holes.
