BMI Calculator
Body Mass Index from height + weight, with WHO categories and an honest note about what BMI does and doesn't measure.
Quick answer: Body Mass Index from height + weight, with WHO categories and an honest note about what BMI does and doesn't measure.
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Frequently asked questions
- How do I calculate my BMI?
- Enter your height and weight in metric (cm + kg) or imperial (ft + in + lb). The tool divides weight by height squared and shows your BMI plus the WHO category — instantly.
- What's a healthy BMI?
- Per WHO: under 18.5 is underweight, 18.5–24.9 is healthy weight, 25–29.9 is overweight, and 30 or more is obese (broken into Class I, II, and III at 30, 35, and 40).
- Is BMI reliable?
- BMI is a simple population screening tool — it works well for most people but doesn't measure body composition. People with a lot of muscle (athletes) can score "overweight" without excess body fat.
- What's the difference between BMI and body fat percentage?
- BMI uses only height and weight. Body fat percentage measures the share of your weight that is fat, using methods like skinfold calipers, bioelectrical impedance or DEXA scans. Body fat % is more accurate but harder to measure.
- How do I calculate BMI for children?
- Children are assessed using BMI-for-age percentiles, not the adult cut-offs. Use a paediatric chart instead — adult BMI categories don't apply under 18.
- What if I have a lot of muscle mass?
- Muscle is denser than fat, so muscular athletes often land in "overweight" by BMI without excess fat. Combine BMI with a body fat measurement (or just a measuring tape around the waist) for a more honest read.
- Which units can I use (cm/kg or in/lb)?
- Both. Toggle between Metric (cm + kg) and Imperial (ft + in + lb) at the top — the math is the same, just expressed differently.
- Can I include age in the BMI calculation?
- Standard adult BMI is age-independent for ages 20+. Some health authorities adjust the healthy range slightly upward for older adults; this tool uses the WHO standard categories.
- Why does BMI differ between countries or guidelines?
- Some countries (notably in East Asia) use lower thresholds because health risks rise at lower BMI in those populations. Our tool uses the WHO international thresholds.
- Can I track my BMI over time?
- This tool shows a single calculation. Bookmark the page and re-run it monthly — many people prefer to track waist measurements alongside BMI for a fuller picture.