  We describe how the out-of-plane dielectric polarizability of monolayer
graphene influences the electrostatics of bilayer graphene -- both Bernal (BLG)
and twisted (tBLG). We compare the polarizability value computed using density
functional theory with the output from previously published experimental data
on the electrostatically controlled interlayer asymmetry potential in BLG and
data on the on-layer density distribution in tBLG. We show that monolayers in
tBLG are described well by polarizability $\alpha_{exp} = 10.8
\unicode{x212B}^3$ and effective out-of-plane dielectric susceptibility
$\epsilon_z = 2.5$, including their on-layer electron density distribution at
zero magnetic field and the inter-layer Landau level pinning at quantizing
magnetic fields.
