Traditional measures

There are a number of different approaches to measuring obesity.

The most common approach to measuring obesity is the Body Mass Index (BMI), which is calculated by dividing a person’s weight in kilograms by his or her height in metres squared (kg/m2). This value is then matched to a weight classification on a BMI chart, where underweight, normal weight, overweight and obesity are defined based on specific cut-offs.

BMI measurements are the same for both sexes and for all ages of adults. Your BMI can be a good starting point in assessing your weight, however it should be considered more of a rough guide, rather than a way to determine if you have obesity, as body composition and distribution of body fat in people with similar BMIs can vary widely.

BMI is a measure of size – not of health!

How to make sense of BMI

BMI is a commonly used method to measure obesity in adults. The different BMI classifications for Caucasians are as follows (lower cut-offs apply to people of East or South Asian origin):

Underweight <18.5
Normal range 18.5–24.9
Overweight 25–29.9
Obesity 30–39.9
Severe obesity ≥40

Waist Circumference Risk Threshold

Health is not determined by the amount of body fat alone but also by where the fat is located. While fat located inside your abdomen (belly-fat) is an important risk factor for diabetes, hypertension, heart disease, fatty liver and other metabolic problems, the fat on your hips and thighs are less associated with health problems. This is why some researchers suggest measuring waist circumference to determine obesity related health risks. In Caucasians, a waist circumference of more than 35 inches in females and more than 40 inches in males suggests that an individual is at a higher risk of developing metabolic problems related to obesity.

Two gradient color scales labeled "european" and "asian or hispanic" show waist circumference norms, with higher values for men than women in both categories.

Newer approaches

While traditional approaches generally rely on individual, physical measurements to assess obesity, newer methods look to take a more comprehensive approach to assessing obesity. The Edmonton Obesity Staging System (EOSS) uses clinical assessments of medical, mental and functional impact of obesity on a person to determine obesity-related health risks and is a far better predictor of mortality than BMI or waist circumference.

Color-coded chart showing five stages of disease progression: stage 0 to stage 4, ranging from "no apparent risk factors" to "end-stage.