What is BMI?
Body mass index (BMI) is one of many factors that you and your health care provider can use to assess your health. It is a quick screening tool for assessing health risk based on your height and weight.
Depending on your BMI number, you will be classified as:
Underweight (BMI less than 18.5)
Healthy weight (BMIs 18.5 to 24.9)
Overweight (BMIs 25 to 29.9)
Obese (BMI 30 and over)
If your BMI is less than 18.5, you are underweight. Health risks associated with being underweight include osteoporosis, infertility, and impaired immune functioning. Underweight may also indicate an eating disorder or other underlying illness.
If your BMI is 18.5 – 24.9, it is a healthy range. This may lower your risk for developing weight-related health problems.
If your BMI is 25 or higher, you are at greater risk of developing diabetes, heart disease and some types of cancer. The higher your BMI number (over 25) is, the greater your risk of developing these conditions.
How is the BMI calculated?
The BMI is calculated using your height and weight. The BMI formula is list below. BMI can be calculated using either metric or imperial measures (the results will be the same).
kilograms (kg) and meters (m)
Weight in kg
(Height in meters)2
Imperial (British) Units
pounds (lbs) and inches (in)
Weight in pounds x 703
(Height in inches)2
BMI is a handy tool, but it is not right for everyone. It may not accurately assess health risks in:
What should I do if my BMI is not within the healthy weight range?
If your number falls in the “overweight” or “obese” BMI range, try to lose weight by making lifestyle changes. Start by eating smaller food portions and increasing your activity level. For information on healthy eating, talk to a registered dietitian. Find a registered dietitian in your area: