A universal methodology to obtain the termination rate coefficients in free radical polymerization as a function of conversion and chain length was used to describe the RAFT-mediated "living" radical polymerization (LRP) and conventional free-radical polymerization (FRP) of methyl methacrylate (MMA) up to the glass regime. A composite termination model determined previously using the reversible addition-fragmentation chain transfer-chain length dependent-termination (RAFT-CLD-T) method, based on conversion (x) and chain length (i) dependent termination rate coefficient, k(t)(i,i) (x), data, was the key parameter in obtaining accurate fits to the experimental rate and molecular weight data. Two kinetic modeling approaches were used in this study: (i) model 1: full chain length distributions; (ii) model 2: "method of moments". Both approaches gave excellent agreement with experimental results for the evolution of conversion and MWD for RAFT-mediated polymerizations and accurately described the kinetics after the gel onset conversion. The simulations were also used to validate the accuracy of the RAFT-CLD-T method up to the glass regime to obtain accurate k(t)(i,i) (x) data. Importantly, our simulations gave excellent fits to the rates of polymerization and MWDs for conventional FRP (with broad MWDs), especially the transition from dilute to the gel regime. There is little or no "short-long" termination in RAFT-mediated polymerizations, and therefore the RAFT-CLD-T method provides an ideal approach to probe the mechanism for termination between chains of similar length and their interaction with the polymerizing matrix up to high conversion. We envisage this modeling framework can be easily applied to many other monomers or free radical systems (e.g., ATRP and NMP) and therefore allow highly accurate predictions of polymerization rates and MWDs.