This paper presents a comparison between the read range of classical RFID and chipless RFID in free space and real environments. From the presented model, read range is derived using analytical formulation over non-isolated channels for both technologies. The paper shows that the well known bounds classically used in free space cannot be achieved in real environments i.e., subjected to leakage, coupling and/or reflections) and therefore need to be modified. Although the introduced bound for semi-passive tags is close to the one corresponding to free space, we show however that for chipless tags read range can not be predicted by the radar equation and presents severe limitations since these tags are linear time-invariant systems. This new bound does not depend on the transmitted power nor the reader sensitivity but relies on the concept of residual environment. We show that, this quantity is the key parameter to evaluate the read range of a chipless RFID system. Moreover, the residual environment can easily be estimated or measured for any reading system. We show that the proposed bound can accurately predict the read range of a chipless system in different environments from anechoic chamber to non-stationary real environments. Results are confirmed in simulation and measurements where difference between theoretical read range and the measured one is only 20 cm.