  We study the butterfly effect of the AdS planar black holes in the framework
of Einstein's general relativity. We find that the butterfly velocities can be
expressed by a universal formula $v_{\rm B}^2 = TS/(2V_{\rm th} P)$. In doing
so, we come upon a near-horizon geometrical formula for the thermodynamical
volume $V_{\rm th}$. We verify the volume formula by examining a variety of AdS
black holes. We also show that the volume formula implies that the conjectured
reverse isoperimetric inequality follows straightforwardly from the null-energy
condition, for static AdS black holes. The inequality is thus related to an
upper bound of the butterfly velocities.
