Surface stress and energy are basic quantities in the Gibbsian formulation of the thermodynamic description of surfaces 1-3 which is central in the formation and long-term behaviour of materials at nanoscale. However, their size-dependence is a puzzling issue. It is even unclear whether they decrease 4-6 or increase 7,8 with decreasing particle size. In addition, for a given metal, estimates often span over an order of magnitude, far apart from bulk data, which, in the absence of any explicit size-dependence rule, escapes understanding. Here, we combine X-ray absorption and nanoplasmonics data with atomistic simulation to describe α-Al 2 O 3 (0001)-supported silver particles. By comparison to MgO(001)-supported 9 and embedded 10 silver, we distinguish epitaxial and surface stress. The latter is shown to dominate above 3 nm in size. Since the observation mostly relies on surface/bulk ratio, a metal-independent picture emerges that