Your BMI is calculated by dividing weight in kilograms by height in metres squared.

BMI = Weight (Kg)/Height^2 (Metres^2)

For example, a woman 1.67m in height and weighing 65kg would have a BMI of 23.3

BMI = 65/1.67x1.67
BMI = 23.3

This example BMI falls within the healthy weight range.

Overweight is measured as 25 or more

& Obesity determined as 30 or more.

What your BMI means
Once you have measured your BMI, you can determine your healthy weight range.

If you have a BMI of:
Under 18 – you are very underweight and possibly malnourished.
Under 20 – you are underweight and could afford to gain a little weight.
20 to 25 – you have a healthy weight range for young and middle-aged adults.
26 to 30 – you are overweight.
Over 30 – you are obese.

For older Australians over the age of 74 years, general health status may be more important than being mildly overweight. Some researchers have suggested that a BMI range of 22-26 is acceptable for older Australians.

Some exceptions to the rule
BMI does not differentiate between body fat and muscle mass. This means there are some exceptions to the BMI guidelines.
Muscles – body builders and people who have a lot of muscle bulk will have a high BMI but are not overweight.
Physical disabilities – people who have a physical disability and are unable to walk may have muscle wasting. Their BMI may be slightly lower but this does not necessarily mean they are underweight. In these instances, it is important to consult a dietitian who will provide helpful advice.
Height – for people who are shorter (for example Asian populations), the cut-offs for overweight and obesity may need to be lower. This is because there is an increased risk of diabetes and cardiovascular disease, which begins at a BMI as low as 23 in Asian populations.

Therefore the BMI is not the best measure of fatness or health risk. Increasingly experts believe that the type of fat and where it is on your body may be more important than BMI – and that your waist circumference is really the figure that you should pay attention to.

If you have a waist measurement above 94cm for men and 80cm for women you may be at risk of serious chronic disease...read more on waist measurement here