The chain-length dependence of the termination rate coefficient, k(t), in butyl acrylate free-radical polymerization has been determined by two independent methods, RAFT-SP-PLP and RAFT-CLD-T, both employing control of radical chain length by reversible addition fragmentation chain transfer (RAFT) polymerization. Within RAFT-SP-PLP, the polymerization induced by a laser single pulse is monitored via near-IR spectroscopy with a time resolution of microseconds. In RAFT-CLD-T, isothermal reaction rate measurements are carried out via DSC under stationary polymerization conditions. The resulting k(t) data refer to the situation of living/controlled radical polymerization, where both radical chain length and monomer conversion increase during the course of the reaction. The RAFT-SP-PLP measurements were carried out at 60 degrees C and two pressures, 5 and 1000 bar. The RAFT-CLD-T experiments were run at ambient pressure and at two temperatures, 60 and 80 degrees C, respectively. In absolute value, the termination rate coefficients for identical pressure and temperature deduced from the two methods differ by less than a factor of 2. For the dependence of k(t) on chain length, i, almost identical information is provided by the two techniques. The chain-length dependence of kt may be described by the power-law expression k(t)(i) = k(t)(1,1)i(-alpha) with, however, a being different for short-chain and long-chain radicals. RAFT-SP-PLP yields alpha(1) = 1.25 for the short-chain regime from 1 < i < 30, and alpha(2) = 0.22 for chain lengths above i = 50. RAFT-CLD-T results in alpha(1) = 1.04 and alpha(2) = 0.20 in identical chain length regimes. kt(1,1) values are found to be close to 1 x 10(9) L mol(-1) s(-1).