Body mass index (BMI) is a health screening tool that has been used since the mid 19th century as a way to analyze your body size and predict body fat. Using a ratio of your weight to your height, the BMI formula will tell you your current weight status - underweight, healthy weight, overweight, or obese. It is one of the few methods widely available to measure obesity in individuals and in large populations and is used worldwide by the Centers for Disease Control (CDC).

For men and women over the age of 18, your body mass index is calculated based on your current height and weight using a basic formula. This can be done using kilograms and centimeters or using pounds and inches, using one of the following two equations. 

• weight (kg) / [height (m)]2
• weight (lb) / [height (in)]2 x 703

You can also easily determine your weight in kilograms by taking your weight in pounds and diving by 2.2 and multiplying your height in inches by 0.0254 to get your height in meters.  

Your BMI index or score represents the proportion of your weight to your height and provides you a single numerical output that can be used to see where you fall on the BMI chart.