Body Mass Index (BMI) and Waist

BMI Calculator

Height (cm)  Weight (kg) 

Your BMI is  

BMI is a calculation that is very well suited to assessing the levels of overweight and obesity across large populations. 

It is calculated by:

BMI = weight(kg) ⁄ height(m)2

Classification of weight by BMI

Classification BMI (kg/m2) Risk of co-morbidities and related disease
Underweight <18.5 Low (but possibly increased risk of other clinical problems)
Normal Range 18.5 – 24.9 Average
Overweight >25.0  
Pre-obese 25.0 – 29.9 Increased
Obese I 30.0 – 34.9 Moderate
Obese II 35.0 – 39.9 Severe
Obese III >40.0 Very severe

BMI calculations are less useful when looking at the health risk of an individual person because BMI calculations will:

  • Overestimate the amount of body fat for people with proportionally high muscle mass e.g.athletes and people of certain ethnicity


  • Often underestimate the amount of body fat for the elderly & people with a physical disability who may have muscle wasting.

Waist measurement on the other hand compares closely with your body mass index (BMI), and is often seen as a better way of checking your risk of developing a chronic disease.

Waist Circumference

Excess weight carried around the abdomen is an independent risk factor for health problems such as: 

  • Heart disease;
  • Type 2 diabetes; and
  • Increased complications of diabetes

When you reduce the amount of fat you carry around your waist (thereby reducing the fat surrounding your internal organs) you are effectively decreasing your risk. Every centimetre that you can lose will help.

A healthy goal for Caucasian people is aim for a waist circumference of:

  • Men: less than 102cm (or 94cm if in a higher risk populations eg for those with
    type 2 diabetes) 
  • Women: less than 88cm (or 80cm if in a higher risk populations eg for those with
    type 2 diabetes) 

At present there is a consensus among diabetes experts that waist circumference targets should be adjusted downwards for Indian, Asian and Aboriginal populations and adjusted upwards for Maori and other Pacific Islander populations, but as yet, no definitive measurements have been determined.

If you are from one of these populations you should speak to your specialist or ask your GP for a waist circumference target that is appropriate for you.

Measurement Technique

It is important to know how to measure your waist correctly so you can follow the same procedure each time – this will make sure that the measurements taken each week can be compared to one another accurately.

To consistently measure your waist circumference, take the tape measure that you received with your phase 1 kit:

  • Find the 'v' shaped notch at the base of your throat and measure straight
    down 35-40cm
  • Measure your belly at this level each time.