  We prove a Carleman estimate for elliptic second order partial differential
operators with Lipschitz continuous coefficients. The Carleman estimate is
valid for any complex-valued function $u\in W^{2,2}$ with support in a
punctured ball of arbitrary radius. The novelty of this Carleman estimate is
that we establish an explicit dependence on the Lipschitz and ellipticity
constants, the dimension of the space and the radius of the ball. In particular
we provide a uniform and quantitative bound on the weight function for a class
of elliptic operators given explicitly in terms of ellipticity and Lipschitz
constant.
