Calculating Your BMI

Body Mass Index, or BMI, is a simple index of weight-for-height that is commonly used to classify underweight, overweight and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in metres (kg/m squared).

BMI = weight (kg) / height (m) x height (m)

The classification of overweight and obesity, according to BMI, is shown in the table below. This applies to men and women over the age of 18.

BMI AND HEALTH

People who are overweight or obese (i.e. a higher BMI), have a greater chance of developing many diseases, such as Heart Disease, diabetes, high blood pressure, and several types of cancer.

BMI AND BODY FAT

BMI does not measure body fat, and cannot differentiate between body fat and muscle mass. People who have the same BMI can have a different percent body fat. For example, a bodybuilder with a large muscle mass and a low percent body fat may have the same BMI as a person who has more body fat, because BMI is calculated using height and weight only.

BMI IN CHILDREN

In adults, BMI changes very little with age. However, in children, BMI changes substantially with age. Therefore, child BMI needs to be assessed using BMI-for-age charts, where the child's BMI is plotted against their age. This will indicate whether the child is underweight, in the normal range, overweight or obese.

BMI CALCULATORS

The following links indicate websites that contain BMI calculators which will tell you what your BMI is, and what weight category you fall into:

Adult BMI:
The Gut Foundation

Child BMI:
Healthy and Active Kids