An early estimate of the potential costs of building a new library is an essential part of the construction planning process. Historical data detailing construction costs for buildings are widely available, but effective use of these data requires an understanding of the difference between “project cost” and “building costs”. Knowledge of the techniques employed to turn generic cost information into data for a specific project is equally important. This article offers some basic information in square foot estimating and will help planners increase the accuracy of pre‐design estimates of project costs.