Fact Files : Measuring BMI - Body Mass Index

Body Mass Index (BMI) is a measure of weight. It is calculated using your height and weight and therefore does not take into account other factors such as fitness, muscle mass and ethnicity. You should use this only as a guide and consult your doctor and dietitian for further analysis of your weight and health risks –, eg blocked arteries, high blood pressure, etc.

To measure your BMI follow the following steps -

1. Measure your height in metres
2 .Measure your weight in kilograms
3. Divide your weight(kg) by height(m)
4. This result is your BMI
5. Refer to the following table to see where you fit.

If you are sitting outside the 'Average' range, it is recommended that you see your doctor and/or dietitian to ensure you are healthy and to help take steps if needed in improving your health.

Limitations associated with the BMI

• Applies to adults aged 18 years and over and are based on studies of Caucasian populations.
• Fat mass in not distinguished from lean body mass/muscle mass. Fat-mass may be underestimated for older adults and overestimated for those with a muscular build (e.g. athletes, bodybuilders).
• Fat distribution is not taken into account.

Measuring your Waist Circumference

Waist circumference can be a useful tool to supplement the BMI. According to the National Institute of Health, waist circumference can give an indication of your risk of developing co-morbidities such as diabetes and raised blood fat levels.

To evaluate your waist circumference, measure around the navel or midway between lowest rib and top of the hip bone (not where your trousers sit) using a measuring tape.

*Reference” World Health Organisation. Obesity: preventing and managing the global epidemic. Report of a WHO consultation. WHO Tech Rep Ser 2000;894(3):i-xii,1-253

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