BMI Calculator
Calculate your body mass index from height and weight — in metric (cm/kg) or imperial — with the WHO category band.
Healthy weight
24.5 BMI
BMI 18.5 – 24.9
A BMI in this range is associated with the lowest population-level health risk for most adults — but it is a single rough indicator, not a diagnosis.
Results update as you type. BMI is a population-level screening tool, not a diagnosis. Athletes, pregnant people, the very tall or very short, and people with very high muscle mass should treat the result with caution.
Formula
BMI is one division:
BMI = weight_kg / (height_m × height_m).
The imperial form folds in the lb→kg and inches→metres conversions:
BMI = (weight_lb × 703) / (height_in × height_in).
Both give the same number for the same person — only the input units change.
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Frequently asked questions
How do you calculate BMI?▾
BMI is weight in kilograms divided by height in metres squared (kg/m²). 75 kg at 1.75 m → 75 ÷ 3.0625 = 24.49. The formula was published by Adolphe Quetelet in 1832; the World Health Organization adopted it in the 1990s as a standard screening figure.
What are the WHO BMI categories?▾
Under 18.5 = underweight; 18.5–24.9 = healthy weight; 25–29.9 = overweight; 30 and above = obesity, split into Class I (30–34.9), Class II (35–39.9), and Class III (≥40). These bands are used across EU member states' national health services, though specific clinical pathways and screening thresholds vary by country and by ethnicity.
Does BMI work for everyone?▾
No. BMI is a population screening tool and is unreliable at the individual level for: athletes and people with high muscle mass (lean weight inflates BMI), pregnant or lactating people (extra weight is normal), the elderly (lean mass decreases with age, so BMI underestimates fat), the very tall or short (the squared denominator distorts at extremes), and children and teens (use age-sex percentiles instead). Treat the result as a starting point, not a verdict.
What about waist circumference?▾
Waist measurement captures fat distribution in a way BMI cannot. WHO thresholds: men with a waist over 102 cm or women over 88 cm have substantially higher cardiometabolic risk regardless of BMI. Some EU countries use lower thresholds (94 cm men / 80 cm women) as the first level of risk; the harmonised IDF metabolic syndrome thresholds are even more conservative for European populations.
Why is BMI used at all if it has so many limits?▾
Because it's almost free to calculate (just height and weight), easy to compare across populations, and reasonably correlated with body fat percentage on average. National health services use it as a screening signal — a high BMI prompts further tests; nobody is diagnosed on BMI alone. More accurate measures (DEXA, hydrostatic weighing, bioelectrical impedance) are slower and costlier.
Are there ethnicity-adjusted BMI bands?▾
Yes — for South Asian, East Asian, and several other ethnic groups, cardiometabolic risk rises at lower BMIs. WHO guidance suggests action thresholds of 23 (overweight) and 27.5 (obese) for these populations, several units below the standard cut-offs. Adopted in clinical practice across many EU countries; ask your GP or specialist for the local protocol if relevant to you.