Body Mass Index (BMI) is a simple screening tool used worldwide to assess whether a person’s weight is appropriate for their height. It is calculated by dividing a person’s weight in kilograms by the square of their height in meters (kg/m²).

The World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and other international health bodies recognize BMI as a useful population-level measure for identifying potential weight-related health risks. However, BMI does not directly measure body fat, muscle mass, bone density, or overall health status.

BMI Formula

BMI = Weight (kg) ÷ Height² (m²)

For example, a person weighing 70 kg with a height of 1.75 meters would have:

BMI = 70 ÷ (1.75 × 1.75) = 22.9 kg/m²

WHO International BMI Classification

BMI (kg/m²)	Classification
Below 18.5	Underweight
18.5 – 24.9	Normal Weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obesity Class I
35.0 – 39.9	Obesity Class II
40.0 and above	Obesity Class III

Why Is BMI Important?

According to the WHO, maintaining a healthy BMI may help reduce the risk of various chronic diseases, including:

• Cardiovascular diseases
• Type 2 diabetes
• High blood pressure
• Stroke
• Certain cancers
• Sleep apnea
• Joint and mobility problems

A BMI outside the healthy range may indicate an increased risk of health complications, although additional assessments are often required for an accurate evaluation.

Limitations of BMI

International health organizations emphasize that BMI is a screening tool, not a diagnostic tool. It may not accurately reflect body composition in:

• Athletes with high muscle mass
• Older adults with reduced muscle mass
• Pregnant women
• Children and adolescents (who require age- and sex-specific BMI percentiles)

Healthcare professionals may use additional measurements such as waist circumference, body fat percentage, and metabolic health indicators alongside BMI.

WHO Recommendation

The World Health Organization recommends using BMI as part of a broader health assessment that includes diet, physical activity, medical history, and other risk factors. Maintaining a BMI within the normal range (18.5-24.9 kg/m²) is generally associated with lower health risks for most adults.

Source: World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), National Institutes of Health (NIH).