What this tool does
BMI is weight divided by height squared. Categories follow common WHO adult cutoffs: underweight below 18.5, healthy range 18.5–24.9, overweight 25–29.9, obesity 30+. Athletes and people with high muscle are often parked in the “wrong” bucket.
How it works
Enter height and weight with the unit toggle. The form converts to kilograms and meters. No sex or age enters the adult BMI formula on this page. That simplicity is why it is used in population work and why it is a blunt personal tool.
Formula and methodology
BMI = weight (kg) / [height (m)]². Adult WHO categories: <18.5, 18.5–24.9, 25–29.9, ≥30. Asian-specific clinical cutoffs sometimes sit lower; this page uses the standard adult bands and does not replace a clinician’s chart.
How to interpret the result
A BMI of 27 on a powerlifter and a BMI of 27 on an inactive person are not the same health story. Use waist, performance, labs, and how clothes fit. If composition is the question, open the Navy body-fat or FFMI tools instead of arguing with BMI.
Example
80 kg at 180 cm: BMI ≈ 24.7 (healthy range). 80 kg at 165 cm: BMI ≈ 29.4 (overweight range). Same mass, different height, different category — still no information about muscle.
Common mistakes
- Using BMI as a competition weight target.
- Calling yourself obese because of a muscular 27.
- Ignoring a rising BMI when waist and fitness are also sliding.
- Applying adult cutoffs to children — this tool is not a pediatric BMI-for-age chart.
When this estimate may be off
- High muscle mass or very low muscle mass.
- Pregnancy, edema, or amputation.
- Older adults whose height has changed from vertebral compression.
- You need body-fat percent or waist-to-height for risk screening.