Body Mass Index (BMI)

*BMI facts medical author: Melissa Conrad Stöppler, MD

• BMI stands for body mass index. BMI is calculated by a formula that takes into account both a person's height and weight.
• BMI is reported as weight in kilograms (kg) divided by height in meters squared (m²).
• BMI is useful in classification of obesity, overweight, and healthy weight.
• Obesity is generally defined as a BMI of 30 or greater, while healthy weight for adults refers to a BMI of at least 19 and less than 25.
• A BMI of 40 or more is often used to identify people who are extremely obese and at risk for serious health complications of obesity.

Body mass index, or BMI, is a new term to most people. However, it is the measurement of choice for many physicians and researchers studying obesity. BMI uses a mathematical formula that takes into account both a person's height and weight. BMI equals a person's weight in kilograms divided by height in meters squared (kg/m²).

It is important to understand what "healthy weight" means. Healthy weight is defined as a body mass index (BMI) equal to or greater than 19 and less than 25 among all people aged 20 or over. Generally, obesity is defined as a body mass index (BMI) equal to or greater than 30, which approximates 30 pounds of excess weight. Excess weight also places people at risk of developing serious health problems.

The table below has already done the math and metric conversions. To use the table, find the appropriate height in the left-hand column. Move across the row to the given weight. The number at the top of the column is the BMI for that height and weight.

Body weight in pounds according to height and body mass index.

Below is a table identifying the risk of associated disease according to BMI and waist size.