Metric & Imperial BMI Body Mass Index Calculator
Calculate Body Mass Index (BMI) using metric (cm/kg) or imperial (ft/lbs) measurements with WHO classification ranges. Includes healthy weight targets, body fat % estimation, BMR, and Ideal Body Weight (IBW) metrics.
Body DimensionsReal-Time Sync
Target where BMI stays within 18.5 – 24.9 for your height.
Medical composite average across Robinson, Devine, Miller, and Hamwi formulas.
Statistical estimation based on BMI, age (30y), and biological sex.
Estimated daily calorie burn for weight maintenance (Mifflin-St Jeor formula).
Volumetric mass ratio
Ratio to upper normal (< 1.0)
2-decimal precision
World Health Organization (WHO) BMI Classification
Standard international clinical diagnostic categories for adult nutritional status
| Category | BMI Range (WHO Global) | BMI Range (Asian Criteria) | Comorbidity Risk Profile |
|---|---|---|---|
| Underweight | < 18.5 | < 18.5 | High (Malnutrition, Osteoporosis) |
| Normal / Healthy | 18.5 – 24.9 | 18.5 – 22.9 | Average / Lowest Risk |
| Overweight (Pre-obese) | 25.0 – 29.9 | 23.0 – 27.4 | Increased metabolic risk |
| Obese Class I (Moderate) | 30.0 – 34.9 | ≥ 27.5 (Obese) | Moderate to high |
| Obese Class II (Severe) | 35.0 – 39.9 | ≥ 32.5 | Severe clinical risk |
| Obese Class III (Morbid) | ≥ 40.0 | ≥ 37.5 | Very severe / morbid risk |
How BMI Is Calculated: Formulas & Mathematics
Height is measured in meters (centimeters divided by 100). For example, a person weighing 70 kg and measuring 175 cm (1.75 m):
Height in feet and inches is first converted to total inches. The factor 703 equates kilograms per square meter from pounds and inches:
BMI is a population-level screening metric and does not differentiate between fat mass, lean muscle, or bone density. Muscular athletes and bodybuilders may register as “overweight” despite having very low body fat, while elderly individuals may register as “normal” despite sarcopenic fat retention.