In this paper, we introduce a novel model, termed as Effective Radius (ER), to calculate the expected number of t-hop neighbors in a multi-hop wireless network with a uniform node distribution on the average. This ER model is an analytical tool that recursively computes a t-hop effective radius for t=2, 3, ⋯. The total number of nodes covered by the disk with a t-hop effective radius equals to the expected number of nodes reachable through at most t hops in the original physical topology. We conduct extensive simulation studies to validate our model and the results demonstrate that the ER model is accurate and can be adaptive to different deployment scenarios. Our findings have interesting applications to the design and evaluation of multi-hop wireless networks.