  Experimental determination of absolute surface energies remains a challenge.
We propose a simple method based on two independent measurements on 3D and 2D
equilibrium shapes completed by the analysis of the thermal fluctuation of an
isolated step. Using then basic equations (Wulff' theorem, Gibbs-Thomson
equation, thermodynamics fluctuation of an isolated step) allows us to extract
the absolute surface free energy of a singular face. The so-proposed method can
be applied when (i) all orientations exists on the equilibrium shape, (ii) the
surface stress is isotropic. This procedure is applied to the case of Si(111)
where we find a value between 0.59 Jm-2 and 0.83 Jm-2 at 1373 K.
