Based on dimensional reasoning of classical turbulence theory, a phenomenological turbulent flame velocity model is proposed. The model explains the whole process of flame development from the inception, through the growth stages to saturation in a simple and unified form. Two sets of mathematical formulae are presented. In formulating the model, the ratios of turbulent to laminar flame velocity are given as functions of the Reynolds numbers based on the integral scale and Taylor microscale, respectively. Comparison of fully developed turbulent flame velocity with experimental results shows good agreement. This model can be easily incorporated in phenomenological models of spark-ignition engines for simulation studies.