How BMI Is Worked Out

BMI compares your weight with your height. Divide your weight in kilograms by your height in metres, multiplied by itself.

For example, a person who is 170 cm tall and weighs 80 kg:

• height in metres, squared: 1.7 x 1.7 = 2.89
• BMI: 80 divided by 2.89 = 27.7, in the overweight range
• healthy weight range for 170 cm: 53.4 kg (a BMI of 18.5) up to 72.1 kg (a BMI of 24.9)

The calculator rounds BMI to one decimal place and uses that figure to pick the range, so the label always matches the number you see. The healthy weight range follows the same rounding, so any weight inside it shows a BMI of 18.5 to 24.9.

Healthy BMI Range for Adults in Australia

The Australian Government Department of Health uses these BMI ranges for adults:

The ranges are the same for women and men. A higher BMI can mean a higher chance of some chronic conditions, such as type 2 diabetes. A BMI under 18.5 can mean you are not getting enough nutrition, which carries its own health problems.

What BMI Misses

BMI is simple to work out, but it is a rough measure. It is a useful guide across a whole population, and less exact for one person.

• Muscle. BMI cannot tell how much of your weight is muscle and how much is fat (healthdirect). People with a lot of muscle, such as body builders, can have a high BMI without being overweight.
• Age. The healthy range is generally higher for older people. For Australians over 70, general health may matter more than being mildly overweight, and some researchers suggest a BMI of 22 to 26 (Better Health Channel). The Nutrient Reference Values suggest a somewhat higher range of 22 to 27 may be warranted for older people. BMI can also under-estimate body fat in older people.
• Ethnicity. The healthy range is generally lower for people of Asian background and higher for people of Polynesian background (Department of Health). Asian and Indian people, for example, carry more body fat at any given BMI than people of European descent, and the risk of diabetes and heart disease can start at a BMI as low as 23 in Asian populations. BMI is also less accurate for Aboriginal and Torres Strait Islander peoples, Pacific Islanders and Maori people.
• Height. BMI tends to over-estimate obesity in shorter people and under-estimate it in taller people, so it is not a guide for adults shorter than 150 cm or taller than 190 cm.
• Other groups. BMI is less accurate in pregnancy, and the adult ranges are not used for children and teenagers under 18. It is also less accurate for people with a physical disability.

Waist Size Adds the Missing Piece

Where your body stores fat matters more than how much you have. A waist measurement is a guide to visceral fat, the fat that coats the organs, which is linked with a higher chance of type 2 diabetes, heart disease and some cancers. It can show this when BMI does not.

Measure halfway between your lowest rib and the top of your hip bone, roughly in line with your belly button, after breathing out normally. These figures do not apply to children or in pregnancy. To learn more, read what visceral fat is and why waist size matters.

If Your BMI Is Above the Healthy Range

For many people, reaching a "healthy" BMI is not realistic, and it does not need to be the first goal. Losing as little as 5% of your body weight can bring health benefits, such as a lower chance of heart disease or type 2 diabetes. For someone who weighs 100 kg, 5% is 5 kg. Outcomes vary between individuals. To track it, see how to calculate your weight loss percentage.

A healthy diet and regular physical activity work together:

• Healthy eating. Build meals from the five food groups: vegetables and legumes, fruit, grain foods (mostly wholegrain), lean meats and alternatives, and milk, yoghurt and cheese or their alternatives (mostly reduced fat). Limit foods and drinks with saturated fat, added salt, added sugars and alcohol, and choose amounts that match your energy needs. For the energy side, read what a calorie deficit is and how to work out yours.
• Physical activity. Australia's guidelines for adults suggest 30 minutes or more of moderate to vigorous physical activity on most days, plus muscle-strengthening activities on 2 or more days a week.

For a step by step plan, see how to lose weight: a realistic guide.

BMI and Weight Loss Treatment

BMI is one of the starting points a registered practitioner looks at when weight loss treatment is discussed, alongside your wider health, history and preferences. It is not a test you can apply to yourself, and two people with the same BMI can receive different advice. To understand the criteria, read who qualifies for weight loss treatment and the BMI criteria. Whether any treatment suits you is decided after an individual assessment, always alongside a healthy diet and physical activity, and outcomes vary between individuals. Read more about weight loss treatment at Burst Health.

Frequently Asked Questions

What is the healthy BMI range in Australia?

For adults, a healthy BMI is 18.5 to 24.9. Under 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is obese, split into three classes. These are the Department of Health ranges. They are a guide only, and the section What BMI Misses above explains where they fit less well.

What is a good BMI for my age?

For adults from 18 to about 70, the healthy range is the same at every age: 18.5 to 24.9. For people over 70, a somewhat higher range may suit, and Australian sources mention 22 to 26 or 22 to 27. Children and teenagers are still growing, so their BMI is read on charts for their age and sex. A GP can tell you which range applies to you.

Is a BMI of 22 considered skinny?

No. A BMI of 22 sits about the middle of the healthy weight range of 18.5 to 24.9. Underweight starts below 18.5. BMI does not show body shape, muscle or where fat is stored, so two people with a BMI of 22 can look quite different. If you are worried about your weight or eating, talk to a GP.

Is 70 kg a healthy weight?

It depends on your height. For an adult, 70 kg falls in the healthy BMI range of 18.5 to 24.9 at heights from about 168 cm to about 194 cm. For someone shorter than about 168 cm, 70 kg gives a BMI above 24.9. Enter your own height and weight in the calculator above to see your BMI and your healthy weight range.

Is reaching a BMI under 25 realistic?

It depends on the person. For many people, reaching a healthy BMI is not realistic, and it does not need to be the only goal. A smaller loss can still bring health benefits, as the section If Your BMI Is Above the Healthy Range explains. Outcomes vary between individuals.

References

• Australian Government Department of Health. BMI and waist. https://www.health.gov.au/topics/overweight-and-obesity/bmi-and-waist
• healthdirect. Body mass index (BMI) and waist circumference. https://www.healthdirect.gov.au/body-mass-index-bmi-and-waist-circumference
• Better Health Channel (Victorian Government). Body mass index (BMI). https://www.betterhealth.vic.gov.au/health/healthyliving/body-mass-index-bmi
• Better Health Channel (Victorian Government). Body mass index calculator for adults. https://www.betterhealth.vic.gov.au/tools/body-mass-index-calculator-for-adult
• Eat for Health (NHMRC). Nutrient Reference Values for Australia and New Zealand: Dietary energy. https://www.eatforhealth.gov.au/nutrient-reference-values/nutrients/dietary-energy
• Eat for Health (NHMRC). Australian dietary guidelines 1 to 5. https://www.eatforhealth.gov.au/guidelines/australian-dietary-guidelines-1-5
• Australian Government Department of Health. Physical activity and exercise guidelines for adults (18 to 64 years). https://www.health.gov.au/topics/physical-activity-and-exercise/physical-activity-and-exercise-guidelines-for-all-australians/for-adults-18-to-64-years

This page is general information only and does not replace individual medical advice. Please speak with a registered Australian healthcare practitioner about your own circumstances.