Life Wellbeing BMI: What is it and how to calculate it

BMI: What is it and how to calculate it

A BMI can give an individual an idea of if they are underweight, healthy or overweight.
A BMI can give an individual an idea of if they are underweight, healthy or overweight. Photo: Getty
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The body mass index or BMI is a value derived from the weight or height of a person.

It is a general tool used to determine if you are a healthy weight compared to your height.

Although this type of tool is used by health professionals, it is only an estimate as it does not take into consideration your gender, age or body composition.

It also does not consider where the weight comes from, like whether it is lean tissue or fat.

How to calculate a BMI

To calculate your body mass index, divide your weight in kilograms by your height in metres.

Then divide the answer by your height again to get your BMI.

If your BMI is above or below the normal range but you consider yourself healthy, check with your doctor for ways to reduce any health risks.

According to the National Health and Medical Research Council, a healthy BMI is between 20-25 for most adults.
According to the National Health and Medical Research Council, a healthy BMI is between 20-25 for most adults. Photo: Bupa 

Are there other measures of body health besides BMI?

Yes, there are several other ways to measure body health.

Body Adiposity Index

BAI multiples your hip circumference by your height. Unlike BMI it doesn’t use your weight in the calculation of determining if you are healthy or not.

For women aged between 20-39 years old, a healthy weight BAI is 21-33 per cent. For 40-50 years old, a healthy weight is 23-35 per cent and for 60-70 year olds it is 25-38 per cent.

For men aged between 20-39 years old, a healthy BAI is 8-21 per cent. For 40-59 year olds, 11-23 per cent is a healthy BAI and for 60-70 year olds, it is 13-25 per cent.

Body Fat Measuring

To calculate your body fat, skin and fat measurements are taken from the waist, biceps and shoulder blades.

The results are added up to produce a single figure that is compared against a chart that shows the patients gender, age and measurements.

The higher the body fat means there is a higher chance of suffering from obesity conditions.

Waist Circumference Measurement

An alternative to BMI is measuring the waist to determine the amount of abdominal fat you are carrying.

According to the Heart Foundation, a waist measurement for most adults greater than 94cm for men and 80cm for women is deemed to be unhealthy.

If the number is greater, this means that a high level of internal fat coats the heart, kidneys, liver, pancreas and digestive organs. This can increase the risk of a stroke or heart disease.

“Carrying excess body fat around your middle is more of a health risk than if weight is on your hips and thighs,” the Heart Foundation said.

To measure your waist, find the top of your hip bone and the bottom of your ribs. Place a tape measure around these parts and check your measurements.