BMI Calculator Calculate Body Mass Index.

The Body Mass Index (BMI) is the most widely used reference value worldwide for assessing whether a person’s body weight, relative to their height, is normal, too low, or too high. The World Health Organization (WHO) has defined four main categories based on BMI: underweight (BMI below 18.5), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obesity (30 and above). This classification has become internationally established in epidemiology and clinical medicine because it is simple to calculate and correlates statistically well with the risk of certain diseases.

The BMI formula is: BMI = body weight (kg) / (height in meters)². For a person weighing 80 kg with a height of 1.80 m, this gives: 80 / (1.80 × 1.80) = 80 / 3.24 ≈ 24.69. This value falls within the normal range. Our calculator performs this calculation automatically as soon as you enter your weight (kg) and height (cm).

An important point: BMI is a statistical population reference value, not an individual diagnostic tool. It accounts for neither muscle mass nor body composition, age, or ethnicity. Strength athletes can have an “elevated” BMI despite a low body fat percentage, because muscle is heavier than fat. Conversely, a normal BMI combined with low muscle mass and high body fat (so-called “normal-weight obesity”) can be misleading. For a well-founded health assessment, further measurements such as waist circumference, body fat percentage, and blood tests are advisable.

In Germany, according to the Federal Statistical Office, a significant share of the population is classified as overweight (BMI ≥ 25). Being overweight, and obesity in particular, increases the risk of type 2 diabetes, high blood pressure, coronary heart disease, stroke, and certain types of cancer. Even a moderate weight loss of 5–10% of body weight can measurably lower this health risk. Being underweight (BMI below 18.5) is also risky and can indicate malnutrition, eating disorders, or serious underlying conditions.