In this paper we use straight‐line models of observed extrinsic nodes to estimate extrinsic stacking‐fault energies. Using isotropic elasticity theory and neglecting interactions, we find simple expressions for the energy in terms of the inscribed radii of the nodes. We apply the results to observed extended nodes in a silver—8 at.% tin alloy and find a ratio of extrinsic to intrinsic stacking‐fault energy of about 3.