BMI Calculator - Free Online Body Mass Index Tool
What is BMI?
BMI (Body Mass Index) is a simple measurement that uses your height and weight to determine if your weight falls within a healthy range. It is the most widely used screening tool endorsed by the World Health Organization (WHO) for assessing weight-related health risks.
This free online BMI calculator instantly shows your BMI score and weight classification — no sign-up required.
BMI Formula
BMI = Weight (kg) ÷ Height (m)²
Example: Height 170cm, Weight 65kg
- BMI = 65 ÷ (1.70)² = 65 ÷ 2.89 = 22.5 (Normal)
BMI Classification Table (WHO Standard)
| Classification | BMI Range | Description |
|---|---|---|
| Underweight | Below 18.5 | May need nutritional support |
| Normal | 18.5 – 24.9 | Healthy weight range |
| Overweight | 25.0 – 29.9 | Weight management recommended |
| Obese Class I | 30.0 – 34.9 | Active management needed |
| Obese Class II+ | 35.0+ | Medical consultation advised |
Note: The WHO standard applies globally. Some regional standards (e.g., Asia-Pacific) use lower thresholds: normal below 23, overweight 23–24.9.
Limitations of BMI
BMI is a useful screening tool but has important limitations:
- Doesn’t account for muscle mass — Athletes may have high BMI but low body fat
- Ignores fat distribution — Abdominal fat (visceral fat) is not reflected
- Age and gender differences — Health risks vary by age and sex at the same BMI
For a more complete picture, consider measuring waist circumference, body fat percentage, and waist-to-hip ratio alongside BMI.
Frequently Asked Questions
Q: My BMI is normal, but I have belly fat. Should I be concerned?
Yes. You can have a normal BMI and still carry excess visceral fat. Men with waist circumference over 102cm (40in) and women over 88cm (35in) should consider fat reduction strategies.
Q: Does age affect BMI interpretation?
The basic BMI formula doesn’t account for age. However, research suggests that for adults over 65, a BMI of 23–27 may actually be associated with better health outcomes.
Q: Can children use this calculator?
This calculator is designed for adults (20+). Children and adolescents should use age-specific BMI percentile charts that account for growth patterns.