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Body Mass Index (BMI)

Body Mass Index (BMI) uses height and weight measurements to determine whether a person is underweight, healthy weight, overweight or obese. BMI is calculated by dividing weight (kg) by height (m) squared.

 BMI = Weight (kg)                
           Height (m) x Height (m)

For example, a woman 1.7m tall weighing 65kg has a BMI of 22.5

BMI  =     65kg           = 22.5kg/m²
               1.7 x 1.7

BMI Classifications

A BMI in the healthy weight range is associated with the lowest risk of disease. These BMI ranges apply to all ethnic groups as the New Zealand Ministry of Health follows the World Health Organisation recommendation not to use specific ethnic BMI ranges.
Note: BMI should be used as a guide only and is not appropriate for people under the age of 18 years, very muscular people, pregnant women or those who are very short (<1.5m) or very tall (>1.9m)


less than 18.5


between 18.5 and 24.9


between 25 and 29.9


30 and above

Waist Circumference

Many people are familiar with the Body Mass Index (BMI) but there is more and more evidence suggesting waist measurement combined with BMI is a better way of determining whether your weight is endangering your health.

If your waist measurement is greater than those listed below you are at increased risk of cardiovascular disease and developing type 2 diabetes. If you have concerns about your BMI or waist circumference, please discuss these with your doctor or a registered dietitian.

Risk of metabolic complications



Average risk



Increased risk



Substiantially increased risk



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