The present work aimed to develop a semi-empirical criterion able to describe impact events on GFRP and CFRP (glass and carbon fiber reinforced polymers) composite thin laminates: these events are able to generate large damages involving multiple mechanisms such as matrix cracking, fiber failure and, above all, delamination. Main purpose of this research was to obtain an accurate numerical description of the impact region in terms of damage extension and depth without the modelization of the adhesive layers. Starting from an experimental campaign of drop-weight impact tests on representative specimens and the implementation of related numerical Ansys LS-DYNA models exploiting equivalent shell approach, a damage criterion was developed and calibrated and a numerical tool was written and implemented within the LsPrePost, evaluating its reliability by means of correlation with the drop tests.