Chain‐length‐dependent termination rate coefficients of the bulk free‐radical polymerization of styrene at 80 °C are determined by combining online polymerization rate measurements (DSC) with living RAFT polymerizations. Full kt versus chain‐length plots were obtained indicating a high kt value for short chains (2 × 109 L · mol−1 · s−1) and a weak chain‐length dependence between 10 and 100 monomer units, quantified by an exponent of −0.14 in the corresponding power law 〈kti,i〉 = kt0 · P−b.