This paper presents the Q factor for use in Adler's formula to estimate locking range of oscillators. We extend it to arbitrary circuit topology, and take into account not only resonator but the entire network. The results show that, even for the same topology, Q differs if we change the port of injection or the active device's property. Since the theory is described in linear Z(ω) matrix domain, it gives oscillator designers a clear vista on their practical circuits.