A comparative approach to studying the spread of policy innovations has recently yielded new and interesting results, as well as theoretical advancements, for policy diffusion research. Specifically, punctuated equilibrium theory has been offered as an explanation for why some policies spread quickly, while others do so normally, and still others are adopted very slowly. Studies of adoption speed, however, currently rely on careful case selection or a dichotomous categorization of adoptions as fast or slow to test why policies diffuse at different speeds. Building on this foundational work, I propose a method for measuring adoption speed as a continuous concept, so that it can be modeled directly as an important outcome of interest to diffusion scholars. I then use the new measure to evaluate how adoption speed varies across time and policy domain. I further demonstrate the utility of the measure as a dependent variable by replicating past results, including the interactive effect of complexity and salience on adoption speed and positive effect of federal incentives, as well as finding preliminary evidence that policy clusters spread more rapidly than the average stand-alone policy.