BMI Chart: Understanding Your Body Mass Index

What Is BMI?

Body Mass Index (BMI) is a screening tool that estimates body fat based on height and weight. The formula is BMI = weight in kilograms divided by height in meters squared. For imperial units, multiply weight in pounds by 703 and divide by height in inches squared.

Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI was designed for population-level studies rather than individual diagnosis. Despite its simplicity, it became the standard screening metric used by health organizations worldwide because it requires no special equipment and provides a quick, reproducible number.

BMI Categories

The World Health Organization defines the following adult categories:

• Underweight: BMI below 18.5
• Normal weight: BMI 18.5 to 24.9
• Overweight: BMI 25.0 to 29.9
• Obese Class I: BMI 30.0 to 34.9
• Obese Class II: BMI 35.0 to 39.9
• Obese Class III: BMI 40.0 and above

For example, a person who is 1.75 meters tall and weighs 70 kg has a BMI of 70 / (1.75 x 1.75) = 22.9, placing them in the normal weight category. A person of the same height weighing 95 kg would have a BMI of 31.0, classified as obese.

These categories correlate with health risks at a population level. Higher BMI is associated with increased risk of cardiovascular disease, type 2 diabetes, certain cancers, and joint problems. Lower BMI may indicate malnutrition or other health concerns.

Limitations of BMI

While useful as a screening tool, BMI has significant limitations that are important to understand.

It does not distinguish between muscle and fat. An athlete with high muscle mass may have a BMI in the overweight or obese range despite having low body fat. A 180 cm bodybuilder weighing 100 kg would register a BMI of 30.9, classified as obese, even though their body composition is predominantly lean muscle.

It does not account for fat distribution. Abdominal fat (visceral fat) poses greater health risks than fat stored in the hips and thighs. Two people with identical BMIs can have very different health risk profiles depending on where their body stores fat. Waist circumference and waist-to-hip ratio provide additional context.

Age, sex, and ethnicity affect interpretation. Older adults tend to have more body fat than younger adults at the same BMI. Women generally carry more body fat than men at equal BMI values. Some ethnic groups face elevated health risks at lower BMI thresholds, which is why some countries use adjusted cutoffs.

Better Together: BMI Plus Other Metrics

Health professionals increasingly use BMI alongside other measurements rather than in isolation. Waist circumference, body fat percentage (measured by calipers, bioelectrical impedance, or DEXA scans), blood pressure, blood sugar levels, and cholesterol panels together provide a far more complete health picture.

BMI remains valuable as an initial screening tool because of its simplicity and accessibility. If your BMI falls outside the normal range, it signals that further assessment may be worthwhile, not that a definitive diagnosis has been made.

Use the health calculators on CalcHub to compute your BMI and other fitness metrics, or try our unit conversion tools to switch between metric and imperial measurements.

Calculate your BMI on CalcHub and get a clearer picture of your health metrics.