What Is BMI and How Is It Calculated?
Body Mass Index (BMI) is a simple screening metric developed in the 1830s by Belgian mathematician Adolphe Quetelet. It is calculated by dividing a person's weight in kilograms by the square of their height in metres (kg/m²). In imperial units, BMI = (weight in pounds × 703) / (height in inches)². BMI is used by the World Health Organization (WHO) and healthcare providers as a quick initial indicator of weight-related health risks.
WHO BMI Categories Explained
The World Health Organization defines BMI categories as: Underweight (BMI < 18.5), which can indicate malnutrition, anemia, or osteoporosis risk; Normal weight (BMI 18.5–24.9), associated with the lowest health risk; Overweight (BMI 25–29.9), indicating excess body fat and elevated cardiovascular risk; Obese Class I (BMI 30–34.9), Class II (BMI 35–39.9), and Class III/Morbid Obesity (BMI ≥ 40), each associated with progressively higher risk of diabetes, heart disease, and hypertension.
Limitations of BMI as a Health Metric
BMI does not distinguish between fat mass and muscle mass. A highly muscular athlete may have a BMI in the 'overweight' range despite having very low body fat. BMI also does not account for fat distribution (visceral fat around organs is more dangerous than subcutaneous fat), age-related changes in body composition, or ethnic variation in body fat distribution. Alternative measures like waist-to-hip ratio (WHR), DEXA scans, and body fat percentage provide more complete pictures.
Healthy Weight Ranges by Height
Healthy weight ranges depend entirely on your height. For a 5'4" (163 cm) person, a healthy weight is 108–145 lbs (49–66 kg). For a 5'10" (178 cm) person, it is 130–173 lbs (59–79 kg). For 6'2" (188 cm), the range is 145–194 lbs (66–88 kg). Use the BMI calculator above to instantly find the exact healthy weight range for your specific height.
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