Exact kink-gas phenomenology at low temperatures

We show that the low-temperature ideal kink-gas phenomenology developed by Currie et al. for the classical statistical mechanics of one-dimensional kink-bearing systems is exact for all potentials in the nonlinear Klein-Gordon family (e.g., sine-Gordon, ${\phi }^4$, double-sine-Gordon, etc.). A general kink-density formula is presented which does not require explicit knowledge of the kink wave form or its small oscillations.