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 and obesity. Figure 1 can be used to calculate your BMI.

Figure 1: BMI calculator and distribution, persons aged 18 and over, by sex, 2017–18

Figure 1: BMI calculator and distribution, persons aged 18 and over, by sex, 2017–18.

This body mass index (BMI) calculator allows you to calculate your BMI by entering your sex, height and weight. These graphs show the distribution of BMI values by sex and the proportion of men and women in each BMI category in 2017–18. The most common category is normal weight (39%) for women and overweight but not obese (42%) for men.

Table 1: BMI classification in adults
BMI (kg/m²) Classification
Less than 18.5 Underweight
18.5 to less than 25 Normal weight
25 or more Overweight or obese
25 to less than 30 Overweight but not obese
30 or more Obese
30 to less than 35 Obese class I
35 to less than 40 Obese class II
40 or more Obese 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
Sex Increased risk Substantially increased risk
men 94cm 102cm
women 80cm 88cm

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