The articulation index (AI) has been widely accepted as an objective measure of environments for speech communication and/or privacy. It quantifies speech intelligibility in terms of the signal‐to‐noise ratio on a scale extending from 0 to 1. While more experimentation is required to verify the subjective equivalent of any given AI, the AI itself can be calculated and hence predicted. It has been found that in buildings without complete floor‐to‐ceiling partitions the AI changes drastically with the following variables: speech effort, speaker orientation, background noise, speaker‐to‐listener distance, and barrier attenuation (if present and unflanked). This paper discusses the relative effect of these variables on the AI, and thus demonstrates the importance of each parameter in the design of open‐plan facilities.