What is one of the most common methods used to assess weight-related disease risk?

More than 6 out of 10 Australian adults are overweight or obese and that figure is rising. Being overweight or obese can cause many serious health problems.

Two methods that are commonly used to estimate whether you are a healthy weight or not are body mass index (BMI) and waist circumference.

Waist circumference is considered a good estimate of your body fat, especially your internal fat deposits, and your likelihood of developing weight-related disease.

Health professionals often use BMI and waist circumference together to assess whether someone is overweight or obese and to assess their risk of cardiovascular disease and diabetes.

What is body mass index (BMI)?

BMI uses weight and height to determine whether an adult is within the healthy weight range, underweight, overweight or obese.

It provides an estimate of total body fat as a proportion of total body weight and the risk of developing weight-related diseases.

BMI is calculated by dividing weight by the square of height as follows:

BMI = Weight (kg)/Height (m)2

healthdirect BMI calculator indicates any health risks in relation to your BMI or waist circumference, and offers information based on your personal results.

If you calculate your BMI yourself, it is important to make sure you measure your weight in kilograms and your height in centimetres.

To find your weight classification (if you are an adult), see which of these BMI ranges your weight falls into:

• Under 18.5: underweight
• 18.5 – 24.9: healthy weight range
• 25.0 – 29.9: overweight
• 30.0 and above: obese

NEED TO LOSE WEIGHT? — Use the BMI Calculator to find out if your weight and waist size are in a healthy range.

Limitations of BMI

BMI is less accurate for assessing healthy weight in some groups of people because it does not distinguish between the proportion of weight due to fat or muscle. BMI is therefore less accurate in certain groups, including:

• certain ethnic groups, such as Pacific Islander populations (including Torres Strait Islander peoples and Maori), Aboriginal peoples, South Asian, Chinese and Japanese population groups
• body builders or weight lifters
• some high-performance athletes
• pregnant women
• the elderly
• people with a physical disability
• people with eating disorders
• people under 18 years
• those with extreme obesity

Why measure waist circumference?

Carrying excess body fat around your middle is more of a health risk than if weight is on your hips and thighs. Waist circumference is a better estimate of visceral fat, the dangerous internal fat that coats the organs. It is therefore a more accurate predictor of cardiovascular risk, type 2 diabetes in women and metabolic syndrome.

How do I measure my waist circumference?

To find out your level of risk, it is important to measure your waist circumference accurately.

1. Place the tape measure directly on your skin, or over no more than 1 layer of light clothing.
2. The correct place to measure your waist is halfway between your lowest rib and the top of your hipbone. This is roughly in line with your belly button.
3. Breathe out normally and measure.
4. Make sure the tape is snug, without squeezing the skin.

Waist circumference and disease risk

These are the waist circumference thresholds that indicate an increased risk of disease:

If you are a woman:

• your risk is increased at 80 cm or more
• your risk is greatly increased at 88 cm or more

If you are a man:

• your risk is increased at 94 cm or more
• your risk is greatly increased at 102 cm or more

Limitations of waist circumference

These waist circumference measurements only apply to adults, not to children. They also do not apply to pregnant women, people with a medical condition involving enlargement of the abdomen, and people from certain non-European backgrounds who may have a different body shape.

What do overweight and obesity mean?

Overweight and obesity are conditions of excess weight that normally result from either excess energy (food) intake and/or insufficient physical activity.

Certain medications and medical conditions can also cause weight gain.

What are the health risks of being overweight or obese?

Being overweight, especially obesity, can increase the risk of a person developing many serious health problems, including:

Many of these diseases can be prevented by maintaining a healthy weight and following a healthy lifestyle, including a well-balanced diet and regular physical activity.

It is encouraging to know that even small amounts of weight loss bring health benefits, including a lower risk of heart disease and type 2 diabetes.

ARE YOU AT RISK? — Are you at risk of type 2 diabetes, heart disease or kidney disease? Use the Risk Checker to find out.

How can I lose weight?

Probably the most successful way to promote weight loss is to have a lifestyle that combines improved nutrition and increased physical activity.

It should also include psychological support — for many people, achieving a ‘healthy’ weight is an unrealistic expectation. A weight loss of 5% (which means losing 5 kg if you currently weigh 100 kg) is more achievable. It will still result in important health improvements.

Your goals should focus on behaviour change and improved health, rather than weight loss.

Some people may need a more intensive approach, such as a very low energy diet, weight loss medication or bariatric surgery. This is especially likely in those who are obese, have other risk factors, or who have been unsuccessful in reducing weight by changing their lifestyle.

How can I reduce my risk of disease?

While Although waist circumference and BMI are important indicators of risk, many other factors also contribute to disease.

There are several other ways to improve your health, including:

Remember, increased physical activity and improved diet will help reduce your risk of disease and have health benefits that are not directly related to weight loss.

Last reviewed: October 2020

• body builders
• some high-performance athletes
• pregnant women.

BMI calculations will underestimate the amount of body fat for:

• the elderly
• people with a physical disability, who are unable to walk and may have muscle wasting.

BMI is also not an accurate indicator for people with:

• eating disorders like anorexia nervosa
• extreme obesity.

Why isn’t BMI always the best measure of health?

Generally speaking, the more body fat you’re carrying, the higher your health risk. However, BMI cannot differentiate between body fat and muscle mass.

This means there are some exceptions to the BMI guidelines:

• Muscles – body builders and people who have a lot of muscle bulk will have a high BMI, but are not overweight.
• Physical disabilities – people who have a physical disability and are unable to walk may have muscle wasting. Their BMI may be slightly lower, but this does not necessarily mean they are underweight. In these instances, it is important to consult a dietitian who will provide helpful advice.
• Height – BMI is not totally independent of height and it tends to overestimate obesity among shorter people and underestimate it among taller people. Therefore, BMI should not be used as a guide for adults who are very short (less than 150 cm) or very tall (more than 190 cm).
• People of different ethnic groups – Asians and Indians, for example, have more body fat at any given BMI compared to people of European descent. Therefore, the cut-offs for overweight and obesity may need to be lower for these populations. This is because an increased risk of diabetes and cardiovascular disease begins at a BMI as low as 23kg/m2 in Asian populations. Some populations have equivalent risks at a higher BMI, such as people of Torres Strait Islander and Maori origin.

What is a healthy BMI range for children?

BMI calculations used for adults are not a suitable measure of weight for children or adolescents. BMI calculations for children and adolescents are interpreted differently from an adult’s and take into account the age and sex of the child or adolescent.

The current BMI charts for children have been developed by the US Centres for Disease Control and Prevention. They are useful for the assessment of overweight and obesity in children aged over two years.

To calculate a child's BMI, you can use the body mass index calculator for children and teenagers.

However, BMI charts should be used only as a guide to indicate when to make small lifestyle changes, and when to seek further guidance from a doctor or a dietitian.

Being overweight or underweight can affect your health

The link between being overweight or obese and the chance you will become ill is not definite. Research is ongoing.

Statistically, there is a greater chance of developing various diseases if you are overweight. For example, the risk of death rises by 20 to 30 per cent as BMI rises from 25 to 27kg/m2. As BMI rises above 27 kg/m2, the risk of death rises more steeply (by 60 per cent).

Risks of being overweight (high BMI) and physically inactive

If you are overweight (with a BMI over 25kg/m2) and physically inactive, you may develop:

Risks of being underweight (low BMI)

If you are underweight (BMI less than 18.5kg/m2), you may be malnourished and develop:

Waist circumference is a better indicator of increased disease risk

A person’s waist circumference is a better predictor of health risk than BMI. When identifying health risk in adults, it is recommended that you combine your BMI classification with your waist circumference as a measurement of disease risk. Having fat around the abdomen or a ‘pot belly’, regardless of your body size, means you are more likely to develop certain obesity-related health conditions. Fat predominantly deposited around the hips and buttocks doesn’t appear to have the same health risk. Men, in particular, often deposit weight in the waist region and therefore have an increased risk of obesity-related disease. Studies have shown that the distribution of body fat is linked to an increased prevalence of diabetes, hypertension, high cholesterol and cardiovascular disease.

Generally, the associations between health risks and body fat distribution are:

• least risk – slim (evenly distributed body fat)
• moderate risk – overweight with no pot belly
• moderate to high risk – slim with pot belly
• high risk – overweight with excess belly fat.

Waist circumference and health risks

Waist circumference can be used to indicate health risk for chronic diseases.

For men:

• 94 cm or more – increased risk
• 102 cm or more – substantially increased risk.

For women:

• 80 cm or more – increased risk
• 88 cm or more – substantially increased risk.

Although the tendency to deposit fat around the middle is influenced by a person’s genes, you can still take this genetic tendency into account and do something about it.

Being physically active, avoiding smoking, and eating unsaturated fat instead of saturated fat have been shown to decrease the risk of developing abdominal obesity.

Where to get help

• Eat for health: Australian dietary guidelines (summary) , National Health and Medical Research Council, Australian Government. 
• About child and teen BMI , US Centers for Disease Control and Prevention. 
• Mooney SJ, Baecker A, Rundle AG 2013, 'Comparison of anthropometric and body composition measures as predictors of components of the metabolic syndrome in a clinical setting ', Obesity Research and Clinical Practice, vol 7, no. 1, pp. 55–66.
• Body mass index – BMI , 2019, World Health Organization (WHO). 

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This page has been produced in consultation with and approved by:

This page has been produced in consultation with and approved by:

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