Clinical BMI Uncertainty Calculator
Calculate body mass index with metric inputs while propagating measurement uncertainty and reporting the WHO weight-status classification.
Educational tool; not a substitute for professional medical judgment.
Examples
- 68.5 kg, 172 cm, ±0.2 kg, ±0.5 cm ⇒ BMI: 23.14 kg/m² (±0.12 kg/m²). Classification: Normal weight.
- 104 kg, 165 cm ⇒ BMI: 38.22 kg/m². Classification: Obesity.
FAQ
What does the uncertainty output represent?
It is the combined standard uncertainty calculated via root-sum-of-squares propagation from the weight and height measurements.
Can I enter imperial units?
Convert pounds to kilograms by dividing by 2.20462 and inches to centimeters by multiplying by 2.54 before entering the values.
How should I round BMI for medical records?
Round BMI to one or two decimals depending on institutional policy; this tool reports two decimals for consistency before you apply local rounding rules.
What if my instruments have different uncertainty definitions?
Enter the standard uncertainty equivalent; if you only have expanded uncertainty, divide by the coverage factor (typically 2) before using the calculator.
Additional Information
- BMI uses kilograms and meters squared; the calculator converts stature from centimeters automatically.
- Uncertainty propagation assumes independent, normally distributed measurement errors and reports one standard deviation.
- WHO adult classifications: underweight <18.5, normal 18.5–24.9, overweight 25.0–29.9, obesity ≥30.0.
- If you omit uncertainty inputs, the tool reports a deterministic BMI consistent with clinical documentation.