BMI Calculator

BMI (Body Mass Index) is a simple measure of body fat based on height and weight. The formula is: BMI = weight (kg) ÷ height (m)². For imperial units: BMI = (weight in lbs × 703) ÷ (height in inches)². It's used as a screening tool, not a diagnostic measure.

According to the World Health Organization (WHO), a normal BMI is between 18.5 and 24.9. Below 18.5 is underweight, 25-29.9 is overweight, and 30 or above is considered obese.

BMI has limitations. It doesn't distinguish between muscle and fat, so athletes or muscular individuals may have a high BMI despite being healthy. It also doesn't account for age, sex, bone density, or fat distribution. It's a useful screening tool but not a definitive health measure.

The WHO defines six categories: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), Obesity Class I (30.0–34.9), Obesity Class II (35.0–39.9), and Obesity Class III (40.0 and above).

For children and teens (ages 2-20), BMI is calculated the same way but interpreted using age- and sex-specific percentiles. A BMI-for-age percentile above 85% is considered overweight, and above 95% is considered obese.

Higher BMI is statistically associated with increased risk of type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers. However, BMI alone doesn't determine individual health — factors like diet, exercise, genetics, and body composition all play important roles.

If your BMI is outside the normal range (18.5–24.9), consider consulting a healthcare provider. They can assess your overall health using additional measures like waist circumference, body fat percentage, blood tests, and lifestyle factors.

Yes, health risk thresholds may differ by ethnicity. For example, the WHO suggests lower BMI cutoffs for Asian populations — overweight at 23+ and obese at 27.5+ — because they tend to have higher body fat percentages at lower BMIs compared to Caucasian populations.