Body Mass Index (BMI) Calculator
Free BMI calculator for Australians. Understand what your BMI means, find your healthy weight range, and get answers to frequently asked questions.
What Is Body Mass Index?
Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate whether you sit within a healthy weight range. Our free calculator lets you determine your body mass index in seconds.
BMI does not measure fat but provides a screening method to identify possible weight problems for adults. It's a quick, widely used tool that helps you and your doctor gauge whether your weight may be affecting your health — but it does not diagnose body fatness or health.
How to Determine Body Mass Index
To determine your body mass index, divide your weight in kilograms by your height in metres squared (BMI = kg ÷ m²). Enter your height and weight in the calculator below and it works out the result instantly, then shows how it compares against Australian health guidelines.
Body mass index formula - enter your details
Enter your height and weight — your BMI updates automatically.
for most adults a healthy BMI is between 18.5 to 24.9 kg/m²
Suggested healthy weight range
Want to talk through your results with a doctor?
Speak with an AHPRA-registered Australian doctor online, 7 days a week. Discuss your health, request a blood test referral, or get advice from home — same-day telehealth appointments.
Book a Telehealth ConsultationAdult BMI categories
The World Health Organisation classifies adult BMI into the categories below. These cut-offs are used internationally, including by Australian health authorities, as a general guide to weight-related health risk.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese class I | 30.0 – 34.9 |
| Obese class II | 35.0 – 39.9 |
| Obese class III | 40.0 and above |
A BMI below 18.5 can point to insufficient nutrition and is linked with lower bone density and reduced immune function. The 18.5–24.9 range carries the lowest statistical risk of weight-related problems for most adults. From 25.0 upward, the risk of conditions such as type 2 diabetes, high blood pressure and cardiovascular disease rises progressively. If your result sits outside the healthy range at either end, a GP can help identify what's driving it and what to do next.
BMI and health in Australia
Nearly two thirds of Australian adults are overweight or obese – BMI is a concern so significant to the nation's health that the Australian Institute of Health and Welfare makes it public enemy number one. It's recorded at GP health assessments and Medicare funded health checks as a baseline for that discussion.
While the standard cut-offs were developed largely from European descendant populations, we know that health risk can present at different BMI levels depending on your background. The WHO as well as Australian guidelines acknowledge this.
BMI ranges for certain populations can be different
Lower numbers carry increased risks for those of Asian, South Asian or Middle Eastern descent. (Overweight and obese thresholds are based on BMI starting at 23 and 27.5 respectively, according to WHO guidelines). For Aboriginal and Torres Strait Islander people, your BMI should be only one factor considered alongside others as part of a holistic and culturally appropriate health assessment. Additionally, for older adults (generally 74+), a slightly higher BMI of around 22–26 may be reasonable. This is because other indicators such as functional health and nutritional intake can become more important than hitting a specific target. Your GP can help you take these factors into account.
About BMI tool and its limitations
Body mass index (BMI) is an internationally recognised standard used to classify the body weight of adults. But BMI isn't a completely accurate measure of body fat content as it doesn't take into account factors such as muscle mass, bone density, body composition, and racial and gender differences.
It is not an appropriate measurement for various groups, including people who are:
- 18 years and under
- 65 years and older
- pregnant
- very muscular
- of various ethnic communities, including people of Asian, Aboriginal or Torres Strait Islander descent
- living with a physical disability
BMI excludes other important measurements of health, such as cholesterol, blood sugar, heart rate, blood pressure and inflammation levels.
Healthy weight range by height
The table below shows the approximate healthy weight range (BMI 18.5–24.9) for common adult heights. Use it as a general reference alongside your own circumstances.
| Height (cm) | Healthy weight range (kg) |
|---|---|
| 150 | 41.6 – 56.0 |
| 155 | 44.4 – 59.8 |
| 160 | 47.4 – 63.7 |
| 165 | 50.4 – 67.8 |
| 170 | 53.5 – 72.0 |
| 175 | 56.7 – 76.3 |
| 180 | 59.9 – 80.7 |
| 185 | 63.3 – 85.2 |
| 190 | 66.8 – 89.9 |
| 195 | 70.3 – 94.7 |
References
- Body mass index (BMI). World Health Organisation. www.who.int/data/gho/data/themes/topics/topic-details/GHO/body-mass-index
- Body mass index (BMI) and waist measurement. Australian Government Department of Health. www.health.gov.au/topics/overweight-and-obesity/bmi-and-waist
- Overweight and obesity. Australian Institute of Health and Welfare. www.aihw.gov.au/reports/overweight-obesity/overweight-and-obesity/contents/about
- Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 2004; 363(9403): 157–163. www.sciencedirect.com/science/article/abs/pii/S0140673603152683
- What's your body mass index (BMI)? National Heart Foundation of Australia. www.heartfoundation.org.au/bmi-calculator
- BMI and all-cause mortality in older adults: a meta-analysis. Am J Clin Nutr, 2014; 99(4): 875–890. pubmed.ncbi.nlm.nih.gov/24452240/
- About Adult BMI. Centers for Disease Control and Prevention. www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
This BMI calculator is a general screening tool for adults aged 18 and over and is provided for information only. It is not a diagnosis and does not replace personalised medical advice. BMI does not apply in the standard way to children, teenagers, pregnant people, or those with high muscle mass. If you have questions about your weight or health, speak with an AHPRA-registered doctor or your GP. MediLeave does not accept responsibility for decisions made based on this tool.
Frequently asked questions about BMI Calculator
What is body mass index?
Body Mass Index (BMI) is a simple measure that uses your height and weight to estimate whether you sit within a healthy weight range. It’s a widely used screening tool that helps you and your doctor gauge whether your weight may be affecting your health. Importantly, BMI does not measure body fat directly and does not diagnose body fatness or health — it simply flags whether your weight is in a range that may warrant a closer look. It also doesn’t account for factors like muscle mass, bone density, age, sex or ethnic background, so it’s best used as a starting point alongside other measures and a doctor’s assessment.
What is the body mass index formula?
The body mass index formula is your weight in kilograms divided by your height in metres squared: BMI = weight (kg) ÷ height (m)². For example, someone who is 70 kg and 1.70 m tall has a BMI of 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2. The formula is the same for men and women and doesn’t change with age. If you prefer to measure height in centimetres, divide by 100 first to convert to metres (170 cm = 1.70 m). The calculator above works this out for you automatically as you enter your height and weight.
What is the relationship between body mass index and obesity?
Body Mass Index is the main screening measure used to identify and classify obesity in adults. Obesity is defined by BMI thresholds: a BMI of 30 or above falls into the obese range, which the World Health Organisation splits into class I (30.0–34.9), class II (35.0–39.9) and class III (40.0 and over). A BMI of 25.0–29.9 is classified as overweight, the band below obesity. So while “overweight” and “obese” describe increasing levels of body weight relative to height, BMI is simply the number used to draw the lines between them.
It’s important to understand that BMI screens for obesity rather than diagnosing it. BMI estimates whether your weight may be too high for your height, but it doesn’t measure body fat directly and doesn’t account for muscle mass, bone density, body composition, age, sex or ethnic background. Someone can sit in the obese BMI range without excess body fat (for example, a very muscular person), and health risk can appear at different BMI levels depending on your background — which is why lower thresholds apply for people of Asian, South Asian and some other descents. For that reason, BMI is best used as a starting point, alongside measures like waist circumference and a doctor’s assessment, rather than as a standalone diagnosis of obesity.
