BMIと体脂肪率計算機

Body Mass Index (BMI) is a simple number calculated from height and weight, first developed by Belgian mathematician Adolphe Quetelet in the 1830s. The World Health Organization uses BMI as a standard screening tool for population-level weight status assessment. It is calculated as: weight (kg) ÷ height² (m²).

WHO defines four main categories: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), and Obese (≥30). Class II obesity starts at 35 and Class III at 40. For Asian populations, the thresholds are slightly lower — overweight begins at 23 and obese at 27.5 due to differences in body composition.

BMI is most accurate for adults aged 20–65. Measure your weight in the morning before eating and after using the bathroom for the most consistent results. Use the same scale each time. If you are heavily muscular (e.g., athletes), pair BMI with waist circumference or body fat percentage for a fuller picture.

BMI does not distinguish between fat mass and lean muscle mass — a professional bodybuilder may register as 'obese' despite low body fat. It also doesn't account for fat distribution: central obesity (belly fat) carries higher cardiovascular risk than peripheral fat. BMI is a screening tool, not a diagnosis. Always consult a healthcare professional for medical interpretation.