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Adult BMI & Body Ratio Calculator (WHO Classification)
Calculate adult Body Mass Index (BMI), Prime BMI, Ponderal Index, and healthy weight targets based on World Health Organization (WHO) clinical classifications.
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Published Last verified
Measurement Units
Enter height in centimeters.
Enter weight in kilograms.
Adult BMI Assessment
Awaiting inputEnter valid positive height and weight measurements above to calculate your adult BMI.
Results, statistical ratios, and detailed amortization ledgers will appear here once values are provided.
Adult Screening Notice: This calculator uses World Health Organization adult criteria (ages 20+). BMI is a screening ratio and does not diagnose disease or measure body fat percentage.
WHO Adult Classification Reference
Severe Thinness< 16.0
Moderate Thinness16.0 – 16.9
Mild Thinness17.0 – 18.4
Normal Weight18.5 – 24.9
Overweight (Pre-obese)25.0 – 29.9
Obesity Class I30.0 – 34.9
Obesity Class II35.0 – 39.9
Obesity Class III (Severe / Morbid)≥ 40.0
HMaintained by Health & Science Tools Desk
Published Last verified
Calculation Methodology & Formula
Metric: BMI = weight (kg) / [height (m)]². Imperial: converted via exact international standard factors (1 in = 0.0254 m, 1 lb = 0.45359237 kg). Ponderal index evaluates volumetric mass: kg / m³.
BMI = weight (kg) / [height (m)]² | BMI Prime = BMI / 25Worked Example: Standard Adult Assessment
Calculate BMI for an adult who is 178 cm tall and weighs 72 kg.
height:178 cm
weight:72 kg
Expected Output22.7 BMI (Normal Weight, Target: 58.6 – 78.9 kg)
72 / (1.78 × 1.78) = 22.72 kg/m², which falls within the WHO normal weight category.
Technical Constraints & Limitations
- BMI is a population screening indicator based purely on weight and height. It does not measure body fat percentage, muscle mass distribution, or visceral adiposity.
- Classifications apply specifically to adults (aged 20+). Pediatric BMI requires age- and sex-adjusted percentile growth charts.
Frequently Asked Questions
What are the adult BMI classifications defined by WHO?
WHO defines: Below 18.5 as Underweight, 18.5 to 24.9 as Normal Weight, 25.0 to 29.9 as Overweight (Pre-obese), 30.0 to 34.9 as Obesity Class I, 35.0 to 39.9 as Obesity Class II, and 40.0 or higher as Obesity Class III.
Why does an athletic individual often register as overweight on BMI?
Muscle tissue is significantly denser than adipose tissue. Muscular athletes often have high BMI numbers despite having very low body fat percentages.
Is BMI used as a medical diagnosis?
No. BMI is strictly an observational screening tool. A comprehensive clinical health assessment requires blood lipid panels, blood pressure, waist-to-hip ratio, and physical evaluation by a healthcare provider.