Body mass index (BMI) is a ratio based on which two measurements?

Body mass index (BMI) is calculated using a person's weight and height, making the correct answer the one that states this relationship. Specifically, BMI is determined by taking an individual's weight in kilograms and dividing it by the square of their height in meters. This formula provides a numerical value that is often used to categorize individuals into different weight status categories, such as underweight, normal weight, overweight, and obese.

The disparity between this answer and the others lies in the fact that options involving age or body composition do not pertain to the BMI formula. While age can impact health assessments and decisions regarding weight, it is not a factor in the calculation of BMI itself. Similarly, body fat and muscle mass can influence an individual's overall health or fitness level, but they are not directly used in the BMI calculation. Thus, the accurate representation of BMI as a measurement is fundamentally anchored in the relationship between weight and height.