Body mass index (BMI)
A weight-to-height ratio used to screen for weight categories.
Body mass index (BMI) is a person's weight in kilograms divided by the square of their height in metres (kg/m²). It's a quick population-level screen that sorts adults into underweight (below 18.5), normal (18.5–24.9), overweight (25–29.9), and obese (30+) ranges. BMI doesn't distinguish muscle from fat, so it can misclassify very muscular people, and it isn't valid for children, pregnant people, or the elderly.