BMI Calculator

What is BMI?

BMI (Body Mass Index) is a simple calculation based on height and weight that categorizes body mass into underweight, normal, overweight, and obese ranges. Developed by Adolphe Quetelet in the 1830s, it uses the formula: BMI = weight (kg) / height (m) squared. It is widely used as a quick screening tool in healthcare, though it has significant limitations.

This tool calculates your BMI and shows where it falls on the WHO classification scale. It also provides context about what BMI means and does not mean, helping you understand this metric's usefulness and limitations for assessing individual health.

How to use this tool

Enter your height and weight in metric or imperial units. The tool calculates your BMI and displays the result with the corresponding WHO category. A visual chart shows where your BMI falls relative to the standard ranges.

BMI categories (WHO)

• Below 18.5 — Underweight. May indicate nutritional deficiency or underlying health issues.
• 18.5 to 24.9 — Normal weight. Associated with the lowest health risks statistically.
• 25.0 to 29.9 — Overweight. Moderately increased risk of cardiovascular disease and diabetes.
• 30.0 and above — Obese (further divided into Class I, II, and III). Significantly increased health risks.

Limitations of BMI

BMI does not distinguish between muscle and fat. A muscular athlete may have a high BMI while having low body fat. It does not account for fat distribution — abdominal fat is more dangerous than fat elsewhere. It does not consider age, sex, or ethnicity — Asian populations face higher health risks at lower BMI values. BMI works better as a population-level statistic than an individual health assessment. For a more complete picture, waist circumference, body fat percentage, and other health markers should be considered.

Frequently asked questions

Is BMI accurate for athletes?

No. BMI cannot distinguish between muscle and fat tissue. Many athletes — especially those in strength sports, football, and rugby — have BMIs in the overweight or obese range despite having low body fat percentages. For these individuals, body fat percentage measured by DEXA scan, calipers, or bioelectric impedance provides a much more accurate assessment of body composition.

Does BMI vary by age and sex?

Standard BMI categories are the same for adult men and women. However, women naturally carry more body fat than men at the same BMI. For children and teens, BMI is interpreted using age-and-sex-specific percentile charts because body composition changes significantly during growth. Elderly adults may benefit from slightly higher BMI (25-27) as some studies show a protective effect of moderate overweight in older age.