Adult screening reference
Adult BMI Calculator
Calculate the adult weight-to-height index and see the corresponding WHO screening category. BMI is a surrogate marker—not a direct measure of body fat or a diagnosis.
Enter an adult height and weight to see the screening index.
WHO adult BMI categories
Underweight
BMI Below 18.5
Normal
BMI 18.5 – 24.9
Overweight
BMI 25.0 – 29.9
Obesity (Class I)
BMI 30.0 – 34.9
Obesity (Class II)
BMI 35.0 – 39.9
Obesity (Class III)
BMI 40.0 and above
BMI (body mass index) is your weight in kilograms divided by the square of your height in metres. The World Health Organization groups adults as underweight below 18.5, normal from 18.5 to 24.9, overweight from 25 to 29.9, and obese at 30 and above — split into Class I (30–34.9), Class II (35–39.9), and Class III (40+).
BMI is a surrogate marker of body fatness, not a direct measurement. WHO notes that additional measures, such as waist circumference, can help with clinical assessment.
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Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). For imperial inputs we convert pounds to kilograms and inches to centimetres first, then apply the same formula.
What are the WHO adult BMI categories?
For adults, the standard reference categories place BMI below 18.5 as underweight, 18.5 to 24.9 as normal range, 25 to 29.9 as overweight, and 30 or above in the obesity classes. These are screening categories, not individual diagnoses.
Is BMI an accurate measure of health?
BMI is a screening index and surrogate marker, not a diagnosis or direct measurement of body fat. Clinical interpretation may also consider body composition, waist circumference, health history, and other measurements.
Does BMI matter for GLP-1 weight management?
BMI can be one data point in a broader clinical assessment, but this calculator cannot determine treatment eligibility or whether a medication is appropriate. A qualified clinician evaluates the full health picture.
Why does this calculator not show a target weight?
Turning a population BMI category into a personal target can overstate what the index can tell you. Weight goals should account for body composition, health history, and clinical context with a qualified professional.
Is BMI the same for men and women?
The BMI formula and the standard WHO category cut-offs are the same regardless of sex. Body composition differs between individuals, however, so BMI should be interpreted alongside other measures and clinical judgment.