BMI Calculator Australia
Calculate your Body Mass Index (BMI) and check your weight category. Use metric (kg/cm) or imperial (lb/in) units. For adults aged 18 and over.
BMI Calculator
Calculate your Body Mass Index (BMI) using metric or imperial units.
| Severe Thinness | 0 – 16 |
| Moderate Thinness | 16 – 17 |
| Mild Thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese Class I | 30 – 35 |
| Obese Class II | 35 – 40 |
| Obese Class III | 40+ |
What Is BMI?
Body Mass Index (BMI) is a simple measurement that uses your height and weight to estimate whether you have a healthy body weight. It is widely used by health professionals as a screening tool to identify potential weight problems in adults. BMI is calculated by dividing your weight in kilograms by the square of your height in metres.
BMI Categories (WHO)
The World Health Organization (WHO) defines the following BMI categories for adults:
| Classification | BMI range (kg/m²) |
|---|---|
| Severe Thinness | 0 – 16 |
| Moderate Thinness | 16 – 17 |
| Mild Thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese Class I | 30 – 35 |
| Obese Class II | 35 – 40 |
| Obese Class III | 40+ |
BMI Formula
Metric formula: BMI = weight (kg) ÷ height² (m²)
Example: 70 kg ÷ (1.75 m)² = 22.9 (Normal)
Imperial formula: BMI = (weight (lb) ÷ height² (in²)) × 703
Example: (154 lb ÷ (69 in)²) × 703 = 22.7 (Normal)
Risks of Being Overweight
A BMI of 25 or higher may increase your risk of health conditions including high blood pressure, type 2 diabetes, heart disease, stroke, sleep apnoea, and certain cancers. Consult your GP to discuss your health and weight.
Risks of Being Underweight
A BMI below 18.5 may indicate being underweight, which can be associated with malnutrition, weakened immune function, osteoporosis, and other health issues.
Limitations of BMI
BMI is a useful screening tool but has limitations. It does not account for body composition, muscle mass, bone density, or fat distribution. Athletes and muscular individuals may have a high BMI but low body fat. Always consult a healthcare professional for a complete assessment.
Frequently Asked Questions
What is a healthy BMI range?
A healthy BMI range for adults is 18.5 to 24.9 according to the World Health Organization.
Is BMI different for men and women?
The same BMI categories apply to both men and women. However, women tend to have more body fat than men at the same BMI.
Is BMI accurate for athletes?
BMI may overestimate body fat in athletes and muscular individuals because muscle weighs more than fat. Alternative measurements such as body fat percentage may be more appropriate.
What is the BMI formula in Australia?
Australia uses the standard WHO formula: BMI = weight (kg) ÷ height (m)². The same categories (underweight, normal, overweight, obese) apply.
Can I use this calculator for children?
This calculator is designed for adults aged 18 and over. For children and teenagers, BMI is calculated using age- and sex-specific percentiles. Consult your GP or use the NSW Health's children's BMI calculator.