Body Mass Index (or BMI)
The Body Mass Index (or BMI) is a calculation of the ratio between your weight and your height. The formula is used to determine the amount of body fat you carry. The formula is your weight divided by your height in meters, squared (BMI = kg/m2). BMI can be used to indicate if you are overweight, obese, underweight or normal.
Proposed classification of weight by BMI in different adult ethnic groups. (2007 Clinical Handbook – New Zealand Dietetic Association, eighth edition - Revised table)
| Classification | NZ European People | Pacific Island & Maori People | Asian & Indian People | Risk of obesity related diseases |
| Underweight | Less than 18.5 | Less than 18.5 | Less than 18.5 | Low |
| Healthy weight | 18.5 - 25 | 18.5 - 26 | 18.5 - 23 | Normal |
| Overweight | 25 - 30 | 26 - 32 | 23 - 25 | High |
| Obese | Greater than 30 | Greater than 32 | Greater than 25 | Very High |
Being overweight or obese puts you at increased risk of developing certain medical conditions associated with obesity.
BMI is meant to broadly categorise groups of people but has it's limitations for use with individuals. Please note the BMI is inappropriate for people under the age of 18 years, pregnant, breastfeeding, taller than 190cm or less than 150cm, an athlete or a body builder
Measuring your waist
To measure your waist circumference, stand with your feet 25-30cm apart with your feet flat on the ground. Your waist measurement should be taken from the narrowest point width-wise, which is usually just above the belly button. Make sure the tape measure is level around your waist then tighten it without depressing the skin. Now take a "normal" breath in. Compare your waist measurement with the table below.
Maximum Acceptable Waist Circumference in different adult ethnic groups (2007 Clinical Handbook - New Zealand Dietetic Association, eighth edition)
| Men | Women | |
| New Zealand European People | Less than 102cm | Less than 88cm |
| Pacific Island and Maori People | Less than 102cm | Less than 88cm |
| Asian and Indian People | Less than 90cm | Less than 80cm |