In D2D-enabled cellular networks, data communications between user equipments (UEs) can be completed by two modes: the cellular mode and the D2D mode where UEs bypass the base station and directly communicate with each other. Usually the transmission mode is selected based on the distance between the UEs. In this paper, the feasible D2D communication distance, i.e., the maximum allowable distance for D2D communications, in a D2D-enabled cellular network is analyzed. To proceed, the coverage probabilities of the cellular and the D2D modes are first derived in closed-forms. Different from prior studies, both the uplink and the downlink transmissions are considered when analyzing the coverage probability of the cellular mode and multi-cell interference is also taken into account in the analysis. Based on the analytical results on the coverage probabilities, the maximum allowable distance for D2D communications is then given in closed-form. The impacts of various system parameters on the maximum allowable distance for D2D communications are finally discussed. The analytical result theoretically justifies the traffic offloading function of D2D communications and shows that D2D communications is applicable especially for modern cellular communication networks where base stations are densely deployed. It also provides an effective guidance on mode selection in D2D-enabled cellular networks.