Cardiac index is the ratio of?

Cardiac index is the cardiac output corrected for the individual's size. For example, the cardiac output of a 50-kg woman will be significantly lower than that of a 90-kg man. It has been found, however, that cardiac output correlates better with body surface area than with body weight. Therefore, it is common to express the cardiac output per square meter of surface area. Under resting conditions, the cardiac index is normally approximately 3 L/min per m2. Ref: Mohrman D.E., Heller L.J. (2010). Chapter 4. Measurements of Cardiac Function. In D.E. Mohrman, L.J. Heller (Eds), Cardiovascular Physiology, 7e