Body mass index (BMI) is widely used in the world, despite caveats concerning its interpretation in relation to gender, age, and race. BMI reading is normally standardized, potentially producing error in the results and classification of nutritional status. Body composition provides more relevant information than BMI: fat mass and lean mass are the main indices. This paper reviews existing equations and proposes the simplest ones and those with the lowest estimation error to replace or complement BMI and improve interpretation of nutritional status and physical activity.