Body mass index (BMI) is a measure of body fat calculated based on a person's weight in relation to their height, and is a simple and inexpensive way to diagnose overweight and obesity. BMI can be used as an easy tool to determine body fat levels by calculating a person's BMI and comparing it to BMI charts, even though it is not fully accurate on its own for measuring body fat. BMI is calculated using the formula of dividing a person's weight in kilograms by the square of their height in meters.