Current methods for planning wireless networks rely on a mixture of on-site measurements and predictive modeling. Unfortunately, such methods can be expensive and time-consuming when it comes to planning for venues of large dimension, or those with a vast number of wireless devices.In this short paper, we focus on an important aspect of scalable network planning: estimating the number of source devices (e.g., access points, base stations) needed to meet traffic demands. We propose a coarse-grained approach that models aggregate demands and interference sources. Minimizing the number of source devices is shown to be NP-complete. However, our coarse-grained approach permits an integer linear program that solves for the optimum while remaining tractable; an approximation result is also derived. Preliminary experiments using QualNet and Ekahau support our approach.