BMI Calculator
Check your Body Mass Index in metric or imperial units and see where it falls on the WHO scale — with honest notes on what BMI can't tell you.
Spotted a mistake or have an idea? — errors get fixed and credited publicly.
Last reviewed: July 20, 2026 · Formulas verified by automated tests before every release.
What BMI measures
Body Mass Index is a quick screening number that relates weight to height. It was designed for tracking populations, and it remains useful for individuals as a first orientation: values far outside the healthy range correlate with higher health risks.
BMI = weight (kg) ÷ height² (m²) · Imperial: BMI = 703 × lb ÷ in²
WHO categories for adults
| BMI range | WHO category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
Limitations to keep in mind
BMI cannot see body composition. Muscular people often have a "high" BMI with low body fat, while a normal BMI can hide low muscle mass. It is also not designed for children and teens (they use age-adjusted percentiles) or during pregnancy.
Disclaimer
This calculator is for general information only and is not medical advice. For an assessment of your individual health, consult a qualified healthcare professional.
Sources, assumptions and limitations
- Formula: BMI = weight (kg) ÷ height² (m²); imperial inputs are converted before calculating
- Assumptions: WHO adult categories; applies to adults 20+, not children, athletes with high muscle mass, or pregnancy.
- Not included: Body composition, fat distribution, ethnicity-specific thresholds — BMI is a screening metric, not a diagnosis; discuss results with a clinician.
- Sources: WHO: A healthy lifestyle — BMI · CDC: About Adult BMI
- Last reviewed: July 22, 2026 by the CalcNotebook team
Frequently asked questions
How is BMI calculated?
BMI = weight in kilograms divided by height in meters squared. In imperial units the formula is 703 × weight in pounds ÷ height in inches squared.
What is a healthy BMI range?
For most adults the World Health Organization defines 18.5–24.9 as the healthy range, 25–29.9 as overweight, and 30 and above as obesity.
Is BMI accurate for everyone?
No. BMI does not distinguish muscle from fat, so athletes can score "overweight" while being lean, and it applies differently to children, pregnant women and the elderly. It is a screening indicator, not a diagnosis.
Should I make health decisions based on BMI alone?
No — BMI is one signal among many. Waist circumference, body composition, blood markers and overall lifestyle matter more. Discuss results with a healthcare professional.