Establishing useful metrics for libraries is not as simple as the oft-repeated ‘measure what matters’ seems to suggest. Useful metrics must balance alignment, objectivity, measurability, and ease of communication. Further, libraries often operate under additional burdens, such as limited data availability and reliance on manual reporting. Mission statements can help anchor and direct a library, but their high degree of abstraction makes measuring success around them difficult. However, there are key attributes of these statements that can help libraries identify the metrics to measure - and guide them toward - success.