  We consider a Fokker-Planck equation in a general domain in ${\mathbb{R}}^n$
with $L^p_{\mathrm{loc}}$ drift term and $W^{1,p}_{\mathrm{loc}}$ diffusion
term for any $p>n$. By deriving an integral identity, we give several measure
estimates of regular stationary measures in an exterior domain with respect to
diffusion and Lyapunov-like or anti-Lyapunov-like functions. These estimates
will be useful to problems such as the existence and nonexistence of stationary
measures in a general domain as well as the concentration and limit behaviors
of stationary measures as diffusion vanishes.
