  We consider the classical obstacle problem on bounded, connected Lipschitz
domains $D \subset \mathbb{R}^n$. We derive quantitative bounds on the changes
to contact sets under general perturbations to both the right hand side and the
boundary data for obstacle problems. In particular, we show that the Lebesgue
measure of the symmetric difference between two contact sets is linearly
comparable to the $L^1$-norm of perturbations in the data.
