Calculating BMI Body mass index (BMI) is a ratio of a person's weight and height. BMI is a tool that you can use to determine whether you are underweight, at a healthy weight, overweight, or obese. Although the calculation is the same for teens and adults, BMI is interpreted differently for the two groups. Part A To find your BMI, enter your weight in pounds and your height in inches in the formula below. Then solve the equation. To check your answer, use this BMI calculator C. Did your calculation match the generated calculation? BMI 703Xweight (lb.) height(in.)