Body mass index

Body mass index (BMI) is used as an indicator of general health. It is calculated taking into account a person's height and weight.

The calculation is: BMI = Weight (kg) / Height² (m)

This calculation categorises people into distinct groups:

• If a person's BMI is less than 18.5 kg/m² then that person is considered 'underweight'.
• If a person's BMI is between 18.5 kg/m² and 24.9 kg/m² then that person is considered 'healthy'.
• If a person's BMI is equal to or above 25 kg/m² then that person is considered 'overweight'.
• If a person's BMI is equal to or above 35 kg/m² then that person is considered 'obese'.
• If a person's BMI is equal to or above 40 kg/m² then that person is considered 'morbidly obese'.

Height-weight tables are used to display this information in a clear manner.

However, calculating a person's BMI is not always the best method of calculating how healthy that person may be. For example, athletes may have higher body mass indices but have a very low body fat. Men are also likely to have a higher body mass index than women of the same height. It is only by considering body composition as a whole that we can get an ideal picture of how healthy or not a person may be. This includes looking at height, weight, gender, age, body fat percentage, frame size and energy expenditure .