What is ideal weight?
Two methods at a glance: WHO BMI and the Broca index
Your ideal weight is not a single number but an individual range that depends on height, gender, age and body type. Our calculator computes two widely used methods at once: the WHO BMI range and the Broca index. Both have their strengths and limitations; together they give a good orientation for the weight range in which you are likely to be in good health.
The BMI-based method from the World Health Organization derives the ideal weight from the normal weight range (BMI 18.5–24.9). Underweight starts at a BMI of 18.5, overweight at a BMI of 25. The corresponding body weights are obtained by multiplying the BMI threshold by the square of the height in meters. For a person 1.80 m tall, this gives: 18.5 × (1.80)² ≈ 59.9 kg (lower bound) and 24.9 × (1.80)² ≈ 80.7 kg (upper bound). That corresponds to an ideal weight range of about 21 kg – a wide corridor that reflects natural variability.
The Broca index, developed by the French surgeon Pierre Paul Broca in the 19th century, is a simpler rule of thumb: normal weight in kg = (height in cm − 100) × 0.9 (men) or × 0.85 (women). For a man 180 cm tall: (180 − 100) × 0.9 = 72 kg. This method is historically widespread and yields a single point value instead of a range. Modern research favors the BMI method, but Broca remains a useful comparison value.
It is important to understand that a healthy weight is not the same for everyone. Muscle mass, body structure, ethnicity and age all play a role. People with a lot of muscle mass can have a higher BMI while still having a low body fat percentage. Older adults often benefit from a somewhat higher weight as a buffer in case of illness. Age-specific percentiles apply to children. Use this calculator as a guide – for an individual assessment, medical advice is essential.