Measuring overweight and obesity

Body Mass Index

Body Mass Index (BMI) is an internationally recognised standard for classifying overweight and obesity in adults. BMI is calculated by dividing a person’s weight in kilograms by the square of their height in metres. 

BMI does not necessarily reflect body fat distribution or describe the same degree of fatness in different individuals. However, at a population level, BMI is a practical and useful measure for identifying overweight or obesity. Figure 1 can be used to calculate your BMI. 

Figure 1: BMI calculator and distribution, persons aged 18 and over, by sex, 2022

This figure calculates your BMI based on sex, height and weight. In 2022, normal weight was highest in women (36%) and overweight only (39%) in men.

Table 1: BMI classification in adults
BMI (kg/m²)Classification
Less than 18.5Underweight
18.5 to less than 25Normal weight
25 or moreOverweight or obese
25 to less than 30Overweight but not obese
30 or moreObese
30 to less than 35Obese class I
35 to less than 40Obese class II
40 or moreObese class III

Source: WHO 2000.

Height and body composition are continually changing for children and adolescents as they grow. Different BMI cut-off points based on age and sex are used when assessing their BMI at a population level (Cole, et al. 2000).

Waist circumference

Waist circumference is an alternative way to assess the risk of developing obesity-related chronic diseases. A higher waist measurement is associated with an increased risk of chronic disease. The threshold at which waist circumference indicates an increased risk of developing disease are dependent on gender and ethnicity (NHMRC 2013). The threshold may also be less accurate in some situations such as pregnancy and medical conditions where there is distension of the abdomen (Heart and Foundation 2023). The risk levels presented below are for Caucasian men and women.

Table 2: Waist circumference associated with increased risk of metabolic complications
SexIncreased riskSubstantially increased risk

Source: NHMRC 2013.

For information on how to correctly measure your waist, visit the National Heart Foundation website,