The pearlite lamellar spacing (λpearlite) is one of the microstructure parameters that define the strength of the lamellar graphite iron (LGI). The transformation kinetics of λpearlite has been the subject of several modeling studies for steels, which demonstrated that the λpearlite can be calculated as a function of undercooling. However, it is hard to find in the literature the models for the prediction of λpearlite in LGI. In the present work, λpearlite in fully pearlitic LGI was investigated for a wide range of carbon contents and cooling rates. The undercooling and the cooling rates were estimated from the experimental cooling curves and were utilized for the prediction of λpearlite. The experimental data analysis provides an empirical expression that correlates λpearlite and cooling rates from the eutectoid transformation region. The developed empirical model was incorporated into a casting simulation software to enable the prediction of λpearlite in LGI and the simulation results were found to be in good agreement with the experimental data.