This article provides a brief review of the Système International (SI) and demonstrates how its routine use for measurements in the ICU might improve education and patient safety in the United States. We apply standard information on SI to common ICU situations. We contrast the confusion and waste from obsolete and/or nonstandard systems of measurement still used in the United States to the clarity and consistency that would result from converting to SI. Examples are drawn from basic weights and measures, electrolyte and other chemical solutions, acid-base physiology, blood gas analysis, BPs, vascular resistances, trauma kinematics, indirect calorimetry, cardiac work, and work of breathing. In addition to simplifying physiologic measurements and relationships, SI provides a common language for international collaboration and communication. Because it would thus improve critical care practice, SI should be increasingly accepted in the United States and especially promoted in the ICU.