This paper introduces a ranging algorithm for wireless sensor networks. Here, a novel time slot based technique is applied for ranging of sensor nodes within the clustered sensor network. The proposed technique avoids clock synchronization of sensor nodes by exploiting the round-trip time-of-flight measurements. Moreover, it is energy efficient as it avoids the complexity inherent in multi-user detection or point-to-point ranging incorporated in traditional round-trip techniques. The performance and feasibility of the proposed method are studied by evaluating the required number of transmissions and receptions and the duration of ranging process.