BMI Calculator

BMI (Body Mass Index) is a simple ratio of your weight to height used as a screening tool for weight categories. It is calculated by dividing your weight in kilograms by the square of your height in meters: BMI = weight(kg) / height(m)^2. For imperial measurements: BMI = (weight in pounds * 703) / (height in inches)^2. While BMI does not directly measure body fat, it correlates well with more direct measures of body fat for most people.

The WHO defines these BMI categories: Underweight (below 18.5), Normal weight (18.5-24.9), Overweight (25.0-29.9), Obese Class I (30.0-34.9), Obese Class II (35.0-39.9), and Obese Class III (40.0 and above). These categories help assess health risks associated with weight. Being in the normal range is generally associated with the lowest risk of weight-related health problems, though individual health depends on many other factors.

BMI has limitations. It does not distinguish between muscle mass and fat mass, so muscular athletes may have a high BMI despite low body fat. It also does not account for age-related muscle loss in older adults, bone density differences, or where fat is distributed on the body. BMI may underestimate body fat in older people and overestimate it in younger, more muscular people. For a more complete health picture, combine BMI with waist circumference, body fat percentage, and other health markers.

For most adults, checking BMI every 3-6 months is sufficient to track trends. More frequent checks (monthly) may be useful if you are actively trying to lose or gain weight. Remember that daily weight fluctuations of 1-2 kg are normal due to water retention, food intake, and other factors. Focus on the overall trend rather than individual readings. If your BMI consistently falls outside the normal range, consult a healthcare provider for a comprehensive health assessment.