Free BMI Calculator Online,
Check Your Healthy Weight Range
Enter your height and weight to see your BMI analysis.
What Is BMI and How Is It Calculated?
BMI, or Body Mass Index, is a number calculated from your height and weight. It is used as a screening tool to identify whether a person is in an underweight, healthy weight, overweight, or obese weight range.
The formula is straightforward: BMI equals weight in kilograms divided by height in metres squared (kg/m²). In imperial units, the formula uses weight in pounds and height in inches, with a conversion factor of 703.
BMI is widely used by healthcare professionals as a quick initial indicator. It is not a diagnostic tool and does not directly measure body fat or overall health. Always consult a healthcare professional for a complete health assessment.
BMI Categories Explained
The World Health Organization (WHO) defines the following BMI categories for adults aged 18 and over:
| BMI Range | Category | General Meaning | WHO Classification |
|---|---|---|---|
| Below 18.5 | Underweight | Below the healthy weight range | Underweight |
| 18.5 to 24.9 | Healthy weight | Within the recommended weight range | Normal weight |
| 25.0 to 29.9 | Overweight | Above the healthy weight range | Pre-obesity |
| 30.0 to 34.9 | Obese class I | Moderate obesity | Obese class I |
| 35.0 to 39.9 | Obese class II | Severe obesity | Obese class II |
| 40.0 and above | Obese class III | Very severe obesity | Obese class III |
Note: These ranges apply to most adults aged 18 to 65. Different thresholds may apply for children, older adults, and certain ethnic groups. Consult a healthcare professional for personalised guidance.
How to Use This BMI Calculator
- 1Select your unit system: choose Metric (cm and kg) or Imperial (ft and lbs)
- 2Enter your height: type your height in centimetres, or feet and inches
- 3Enter your weight: type your weight in kilograms or pounds
- 4Click Calculate BMI: your BMI score and category appear instantly
What Are the Limitations of BMI?
BMI is a useful starting point but has several well-documented limitations:
- It does not distinguish between muscle and fat. A very muscular person may have a high BMI without excess body fat.
- It does not account for where fat is distributed in the body, which affects health risk.
- Standard BMI ranges may not be accurate for all ethnic groups. Some guidelines use lower thresholds for South Asian and East Asian populations.
- It is not designed for children, pregnant women, or adults over 65 without adjustment.
- It is a screening tool, not a diagnosis. A BMI outside the healthy range does not automatically mean a person has a health problem.
Frequently Asked Questions
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For informational use only. Consult a healthcare professional for medical advice.