BMI Calculator Guide
Everything you need to know about using our BMI Calculator and understanding your results.
How to Use the BMI Calculator
- 1
Enter Your Height
Enter your height in centimetres (cm). For example, if you're 5'10", enter 178.
- 2
Enter Your Weight
Enter your weight in kilograms (kg). Use a recent measurement for accuracy.
- 3
View Your Results
Your BMI, classification, and healthy weight range appear instantly.
WHO BMI Classifications
The World Health Organization (WHO) defines the following BMI categories for adults:
| Classification | BMI Range | Health Risk |
|---|---|---|
| Underweight | < 18.5 | Possible nutritional deficiency |
| Normal weight | 18.5 - 24.9 | Lowest health risk |
| Overweight | 25.0 - 29.9 | Increased health risk |
| Obese Class I | 30.0 - 34.9 | High health risk |
| Obese Class II | 35.0 - 39.9 | Very high health risk |
| Obese Class III | ≥ 40.0 | Extremely high health risk |
BMI Formula
Body Mass Index is calculated using this simple formula:
BMI = weight (kg) / height (m)2
Example:
Weight: 75 kg, Height: 175 cm (1.75 m)
BMI = 75 / (1.75 × 1.75) = 75 / 3.0625 = 24.5
BMI Limitations
While BMI is a useful screening tool, it has several important limitations:
- ! Doesn't measure body composition: BMI can't distinguish between muscle, fat, bone, and water weight.
- ! Athletes may be misclassified: Muscular individuals often have high BMI but low body fat.
- ! Age differences: Older adults may have more body fat at the same BMI as younger adults.
- ! Ethnic variations: Different ethnic groups may have different health risks at the same BMI.
- ! Not for children: Children and teens need age-specific BMI percentile charts.
When BMI is Useful
- ✓ Quick screening tool for potential weight-related health issues
- ✓ Tracking weight changes over time
- ✓ Population-level health studies and statistics
- ✓ Starting point for health conversations with your doctor
Additional Health Measurements
For a more complete picture of your health, consider these alongside BMI:
Waist Circumference
Measures abdominal fat. High risk: >94cm (men), >80cm (women)
Waist-to-Hip Ratio
Indicates fat distribution. High risk: >0.90 (men), >0.85 (women)
Body Fat Percentage
Directly measures fat vs lean mass. Requires special equipment.
Blood Pressure
Key indicator of cardiovascular health. Normal: <120/80 mmHg
Consult a Healthcare Professional
BMI is just one indicator. For personalized health advice, weight management plans, or concerns about your weight, please consult with:
- • Your General Practitioner (GP)
- • An Accredited Practising Dietitian (APD)
- • An Exercise Physiologist