Calculate Body Mass Index and weight category
Body Mass Index (BMI) is a measure of body fat based on height and weight that applies to adult men and women. While not a direct measure of body fat, BMI correlates with more direct measures and provides a quick screening tool for weight categories that may lead to health problems.
BMI = weight (kg) / height² (m²) or BMI = weight (lb) × 703 / height² (in²)
| Calculation | Expression | Result |
|---|---|---|
| Normal weight | 70 kg, 175 cm | BMI: 22.9 |
| Overweight | 85 kg, 170 cm | BMI: 29.4 |
| Underweight | 50 kg, 170 cm | BMI: 17.3 |
BMI categories: Below 18.5 = Underweight, 18.5-24.9 = Normal/Healthy weight, 25.0-29.9 = Overweight, 30.0 and above = Obese. These categories indicate potential health risks, with both extremes associated with increased health concerns.
BMI doesn't account for muscle mass, bone density, age, sex, or fat distribution. Athletes may be classified as overweight despite low body fat. It also doesn't distinguish between subcutaneous and visceral fat. Consider it a screening tool, not a diagnosis.
Children's BMI is calculated the same way but interpreted using age and sex-specific percentiles because body composition varies as children grow. A BMI-for-age percentile shows how a child compares to others of the same age and sex.
High BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, high blood pressure, certain cancers, sleep apnea, osteoarthritis, and fatty liver disease. Risk increases with higher BMI, especially above 30.
Low BMI (underweight) can indicate malnutrition, eating disorders, or underlying illness. It's associated with weakened immune system, bone loss, anemia, fertility issues, and increased complications from surgery or illness.
Both have value. BMI is easy to calculate and useful for general screening. Body fat percentage is more accurate for fitness assessment but requires special equipment. For most people, BMI provides adequate guidance, but athletes and those with unusual body composition should consider body fat measurements.