Body mass index (BMI) and waist size: which is better?
Neither. Rather they complement each other by describing different aspects of body size.
What is body mass index (BMI)?
Body mass index (BMI) is calculated from your weight and height.
BMI is calculated by dividing your weight by the square of your height as follows:
BMI = Weight in kilos/Height in metres x Height in metres
You can find your BMI using a BMI calculator. The calculator can give you an idea of any health risks related to your BMI or waist circumference. It also offers information based on your personal results.
Once you know your BMI, you can find your weight classification.
For adults, the BMI ranges and classifications are:
- BMI under 18.5: underweight
- BMI between 18.5 and 24.9: healthy weight range
- BMI between 25.0 and 29.9: overweight
- BMI equal to 30.0 or above: obese
Your BMI is a guide to tell you if you are the correct weight for your height. Your BMI can give an indication of your chance of developing weight-related disease such as diabetes.
What are the limitations of BMI?
BMI is not always accurate for assessing healthy weight in some people. It can’t tell what amount of weight is due to fat or muscle.
BMI is less accurate in the following groups of people:
- certain ethnic groups (e.g. Black and aboriginal people)
- body builders or weightlifters
- some high-performance athletes
- pregnant women
- people with a physical disability
- people under 18 years.
Why measure waist size?
People carry fat in different parts of their bodies. Some people carry extra body fat around their middle. This is more of a health risk than carrying weight on your hips and thighs.
Waist circumference is a better estimate of ‘visceral fat’. This is the dangerous internal fat that coats your organs.
Measuring visceral fat can give a more accurate predictor of some health conditions. These include:
- Cardiovascular disease risk
- Metabolic syndrome
- Type 2 diabetes
Waist size and disease risk
These are the waist size thresholds that indicate an increased risk of disease:
If you are a female:
- Your risk is increased if your waist measurement is 32 in (80 cm) or more
- Your risk is greatly increased if your waist measurement is 35 in (88 cm) or more.
If you are a male:
- Your risk is increased if your waist measurement is 37 in (94 cm) or more
- Your risk is greatly increased if your waist measurement is 40 (102 cm) or more.
