Abstract Recognizing the persistent inaccuracy of existing linear and nonlinear expressions to extract laminar flame speeds from experimental data of stretched flame speeds, and the essential and independent role of the flame thickness, in addition to the laminar flame speed, in describing the coupled diffusive and reactive response of the laminar flame structure and propagation, we have adopted the finite flame thickness expression of Frankel and Sivashinsky in the extrapolation. Using numerically generated stretched flame data of the outwardly expanding spherical flame for both lean and rich hydrogen/air and n-heptane/air mixtures, it is demonstrated that the finite thickness expression yields not only improved extraction of the laminar flame speed, it also collaterally yields the laminar flame thickness as well as the Markstein length. Additionally, we have examined the cause for the inaccuracy of the pervious linear and nonlinear extrapolation expressions, the effects of pressure on the extrapolation results, and the robustness of the various expressions in accounting for the experimental errors.