Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. 1. Enter your weight, height and Age using standard or metric measures ,Gender Selection is Optional. 2. Select "Calculate BMI" and your BMI will appear. The Body Mass Index (BMI) Calculator can be used to calculate BMI value and corresponding weight status while taking age into consideration. Use the "Metric Units" tab for the International System of Units or the "Other Units" tab to convert units into either US or metric units