BMI Calculator — Free Body Mass Index CalculatorMetric & Imperial · WHO BMI Classification · Adults 18+
Use this free BMI Calculator to instantly calculate your Body Mass Index (BMI) using your height and weight in either metric (kg / cm) or imperial (lbs / inches) units. BMI is a globally recognized body weight screening tool developed by the World Health Organization (WHO) and used by clinicians, dietitians, and public health professionals worldwide to classify adults into standard BMI weight categories: Underweight (BMI below 18.5) · Normal weight (BMI 18.5–24.9) · Overweight (BMI 25–29.9) · Obese (BMI 30 and above). This online BMI calculator for adults uses the standard BMI formula — BMI = weight (kg) / height² (m²) — to deliver an instant BMI score alongside your healthy weight range, helping you assess weight-related health risks including cardiovascular disease, type 2 diabetes, hypertension, and metabolic syndrome. For a more complete assessment of body composition, combine your BMI result with waist circumference, body fat percentage, and a consultation with a qualified healthcare professional.
⚠ Medical Disclaimer: This BMI calculator is intended for informational and educational purposes only. BMI is a screening tool — not a diagnostic measure — and does not account for muscle mass, bone density, age, ethnicity, or body fat distribution. Results should not replace a professional medical evaluation or advice from a licensed doctor, dietitian, or healthcare provider.
Related Health Calculators
BMI Calculator — Body Mass Index and What the Categories Actually Mean
Body Mass Index (BMI = weight(kg) / height(m)²) is a population-level screening tool that correlates with body fat at the group level but is an imperfect measure for individuals. A BMI of 18.5-24.9 is classified as normal weight; 25-29.9 as overweight; 30+ as obese. The BMI calculator converts between metric and imperial units and places the result on the WHO classification scale. For adults, BMI works reasonably well as a first-pass indicator, though it systematically misclassifies muscular athletes (falsely high BMI), older adults with muscle loss (falsely normal BMI), and certain ethnic groups with different fat distribution patterns.
BMI interpretation differs by age and sex in children and adolescents, where the same BMI value represents different percentiles depending on age and gender. The growth chart context is essential for pediatric BMI — a BMI of 17 might be normal for a 5-year-old but below the 5th percentile for a 15-year-old. The calculator applies age- and sex-specific percentile tables for users under 20, producing a percentile result rather than a fixed category.
BMI alone does not assess metabolic health or cardiovascular risk as well as BMI combined with waist circumference. A person with normal BMI but large waist circumference (>40 inches for men, >35 inches for women) faces elevated metabolic risk — a pattern called "normal weight obesity" or "thin fat." Conversely, a person with BMI 27 but low waist circumference and high muscle mass may have lower health risk than their BMI suggests. The calculator notes waist circumference thresholds alongside the BMI result for a more complete risk picture.