Body mass index (BMI) is the most commonly used measurement of whether someone is a healthy weight. It is obtained by dividing someone’s weight in kilograms (kg) by their height in metres (m), and then dividing the answer by the individual’s height once more.

It is important to remember that BMI is an indicator rather than an absolute assessment. Children, for example, should have their weight considered in relation to their height, age and gender to obtain a BMI centile.

Similarly, BMI is not necessarily a good measure in some groups of adults, such as those who are more muscular and are therefore heavier but healthy (for example, some athletes), and people of Asian origin in whom BMI is often combined with their waist circumference measurement to assess health risk.