When planning and evaluating community-level initiatives focused on policy and environment change, it is useful to have estimates of the impact on behavioral outcomes of particular strategies (e.g., building a new walking trail to promote physical activity). We have created a measure of estimated strategy-level impact--"population dose"--based on our work in evaluating obesity prevention initiatives that uses elements of the RE-AIM method of combining reach and effectiveness to estimate the impact of a strategy on risk behaviors within a target population. We provide a definition and examples of measuring population dose, discuss measurement options in the face of uncertainty about key parameters, review ways of increasing population dose, and illustrate how the concept of population dose has been used in the Kaiser Permanente Community Health Initiative. (Contains 1 table.)