Radio Frequency Identification (RFID) systems consist of fast capturing radio frequency tags and networked electromagnetic readers. Despite the advances of the RFID technology, tag collision is a major problem and can be solved by using the anti-collision scheme. The current ALOHA-based approach suffers from tag starvation problem due to the inaccurate frame size. In this paper, we propose a "RFID Explicit Tag Estimation Scheme" (RETES) for a Dynamic Framed-Slot ALOHA (DFSA), which estimate precise number of tags around the reader and compatible with Electronic Product Code (EPC) Class 1 Generation 2. The preliminary findings indicated that our method achieves better outcome than existing techniques. We identified that the variations of specific RETES's parameters impact the DFSA's performance. Therefore, to achieve the best performance the parameters should be dynamically adjusted over the process of identification.