  Recently, entropy of static supersymmetric black holes in $AdS_6$ was
microscopically counted by the topologically twisted index of five-dimensional
superconformal field theories. However, the AdS/CFT dictionary states that the
partition function of the boundary field theory corresponds to the on-shell
action of the bulk quantum gravity. In this paper, we aim to explain the
microscopic counting of black hole entropy by the topologically twisted index.
We calculate the renormalized on-shell action and show that the on-shell action
equals the Bekenstein-Hawking entropy of the supersymmetric black holes in
$AdS_6$.
