BMI Calculator — Metric & Imperial
Enter your height and weight in either metric (cm / kg) or imperial (ft + in / lb) units. CalcWize returns your BMI and the WHO category (underweight / normal / overweight / obese). BMI is a screening tool, not a diagnosis — it doesn't measure body composition or distinguish muscle from fat.
BMI categories (WHO)
<18.5 underweight · 18.5–24.9 normal · 25.0–29.9 overweight · ≥30 obese (further split into Class I, II, III above 30/35/40). The thresholds were derived from large adult-population studies and don't apply well to athletes, the elderly, or certain ethnicities.
What BMI doesn't measure
BMI uses height and weight. It can't see body fat percentage, muscle mass, fat distribution, bone density, or fitness level — all of which affect what your weight actually means for your health. A 95 kg sprinter and a 95 kg sedentary person of the same height have identical BMIs and very different bodies. Treat the number as the start of a conversation, not the answer.
Better health indicators
Modern guidance pairs BMI with waist circumference, waist-to-height ratio, blood pressure, and resting metabolic markers (lipids, glucose). Those together give a much fuller picture than BMI alone. For sport-context body composition, DEXA scans, calliper testing, or bioelectrical impedance are far more accurate. None of these replace a clinician — but they give a clinician more to work with.
Population caveats
WHO BMI thresholds were derived primarily from European-ancestry adult populations. Some Asian populations show higher cardiovascular and diabetes risk at lower BMI values; many countries (e.g. India, Singapore) use modified cut-offs (overweight from BMI 23+). Children and adolescents use percentile-on-age charts entirely, not the adult thresholds. Pregnancy and elderly individuals also need different benchmarks.
Frequently asked questions
- Is BMI accurate for everyone?
- No. It can’t tell muscle from fat and doesn’t fit athletes, the elderly, children, or every ethnic group well — some populations use lower thresholds. Treat it as a rough screen, not a diagnosis.
- What counts as a healthy BMI?
- The WHO normal range is 18.5–24.9, but it is a population guideline. Waist measurement, blood markers, and fitness give a fuller picture — speak to a clinician for a real assessment.
How we calculate it
BMI = weight (kg) ÷ height (m)². Imperial inputs are converted to metric first. The result is mapped to the standard World Health Organization categories: underweight, normal, overweight, and obese.
What it doesn't do
- Children (different growth-chart percentile system applies)
- Athletes with high muscle mass (BMI overstates obesity here)
- Medical diagnosis (talk to a clinician)
Last reviewed: 2026-05