World Health Organization (WHO) standard BMI classification for adults.
Category
BMI Range
Health Risk
Underweight
Below 18.5
Malnutrition risk
Normal weight
18.5 – 24.9
Low risk
Overweight
25.0 – 29.9
Moderate risk
Obese Class I
30.0 – 34.9
High risk
Obese Class II
35.0 – 39.9
Very high risk
Obese Class III
40.0 and above
Extremely high risk
Frequently Asked Questions
Everything you need to know about BMI.
BMI (Body Mass Index) is a numerical value calculated from your weight and height. It is widely used as a screening tool to identify possible weight categories that may lead to health problems. BMI is calculated by dividing your weight in kilograms by the square of your height in metres (kg/m²).
BMI is a useful screening tool but it has limitations. It does not directly measure body fat and may overestimate it in muscular individuals (e.g. athletes) or underestimate it in older people who have lost muscle mass. Always consult a healthcare professional for a complete health assessment.
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, optimal ranges can vary by age, sex, and ethnicity. Asian populations, for example, may have higher health risks at lower BMI values.
Using metric units: BMI = weight(kg) ÷ height(m)². For example, if you weigh 70 kg and are 1.75 m tall: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9. Using imperial: BMI = (weight(lb) ÷ height(in)²) × 703.
BMI for children and teenagers is calculated the same way but interpreted differently using age- and sex-specific percentile charts, since body fat changes with age and differs between boys and girls. This calculator is designed for adults aged 18 and above.