BMI Calculator
Calculate your Body Mass Index (BMI) and find your classification according to WHO. Enter weight and height for an instant result.
Your BMI
WHO classification table
What is BMI?
Body Mass Index (BMI) is a measure adopted internationally to assess whether a person's weight is appropriate for their height. It is calculated like this: BMI = Weight (kg) ÷ Height² (m²).
As an epidemiological reference, BMI helps a lot, but it does not replace evaluation by a doctor, since it ignores body composition and cannot tell muscle apart from fat.
Body Mass Index (BMI): formula and ranges
BMI is defined as BMI = mass / height² with mass in kilograms and height in metres, giving units of kg/m². For a person weighing 70 kg at 1.70 m: 70 / (1.70)² = 70 / 2.89 ≈ 24.2 — within the normal range. The WHO classifies adults as: < 18.5 underweight; 18.5–24.9 normal; 25.0–29.9 overweight; 30.0–34.9 obesity class I; 35.0–39.9 class II; ≥ 40 class III (severe). The index was proposed by Adolphe Quetelet in 1832 and renamed "Body Mass Index" by Ancel Keys in 1972.
BMI is a population-level screening tool, not a diagnosis. It does not distinguish muscle from fat — athletes and bodybuilders can have BMI in the overweight range without excess body fat — and it does not account for fat distribution. Waist circumference (≥94 cm in men, ≥80 cm in women raises cardiovascular risk) is a better single predictor. Children and adolescents use age- and sex-specific percentile curves.
Clinical context
BMI guides risk stratification for type 2 diabetes, hypertension, cardiovascular disease, sleep apnoea and certain cancers. In Brazil, bariatric surgery is eligible (CFM Resolution 2.131/2015) for BMI ≥ 35 with comorbidities or BMI ≥ 40 without. Older adults may have slightly higher healthy ranges; pregnant women should not use standard BMI.
FAQ
What is a healthy BMI? For adults aged 20+, 18.5 to 24.9 kg/m². Below 18.5 indicates underweight (possible nutritional deficiency); above 25 is overweight.
Why does my BMI look high if I'm muscular? Muscle is denser than fat. Athletes routinely have BMI in the overweight range without health risk. Use body-fat percentage or waist measurement for a clearer picture.
Is BMI useful for children? Not directly. Children use BMI-for-age percentile charts (CDC or WHO) — the same numeric BMI means different things at different ages.
How accurate is BMI as a health measure? Good at the population level, limited at the individual level. Combine with waist circumference, blood pressure, lipid profile and glucose for a real health assessment.
What your BMI really means
Body Mass Index is the most widespread calculation for a quick sense of whether weight matches height. The formula is simple (weight divided by height squared), yet the number on its own says little. What truly counts is the range it falls into. Enter weight and height here and get the figure already classified.
The result is slotted into the World Health Organization ranges: underweight, normal weight, overweight and the degrees of obesity. That helps you read the number instead of staring at it on its own. Remember BMI is a general indicator and doesn't separate muscle from fat, so athletes, for instance, fall outside the pattern.
The calculation comes out right away, runs in the browser and keeps none of your data. Use it as a starting point. For a full health assessment, nothing replaces a professional's guidance.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.