How (and why) to calculate your BMI

Have you ever wondered how to calculate your BMI or why you should?  Many health professionals use BMI as a basic way to determine if someone is within their healthy weight range.  It has been used for many years and is a simple calculation of your height to weight ratio, however people often dismiss BMI as an ineffective metric for a few reasons.

The first one being that they don’t like the result.  If you are given a result in the overweight or obese range, and this has come as an unpleasant shock to you, you are more likely to discredit the metric than to accept the result on face value.  The reality is that 68% of Australians fall into the overweight or obese category, so if you fall into that range you are in the majority.  Whether you self identify as overweight or obese is actually irrelevant to this metric, it is simply a starting point for a bigger conversation about your health.

The BMI formula is actually very simple:

BMI = kg/m²

• kg is a person’s weight in kilograms
• m² is their height in metres squared

Example 60kg/1.75m² = BMI 19.59

Below you can use our calculator to determine your BMI.  Simply plug in your details and it will give you a result and what range you fall into.

Things to keep in mind about BMI:

1. The results are arbitrary and don’t tell you anything else about your state of health
2. BMI skews against short people.  Example 10cm shorter = approx 15% higher BMI for the same weight
3. BMI skews against muscly people (athletes).  Example 10kg heavier = approx 15% higher BMI for the same height
4. None of these are reasons to discredit the metric, simply to keep it in perspecitve

Although we wouldn’t suggest using BMI as a 1 size fits all metric, the information it gives you as part of your overall health data can be useful.  If the calculation puts you just in the overweight or obese range (even if you don’t see yourself that way, or have never weighed less) consider that you are at a higher risk of health complications such as heart attack, type 2 diabetes, and some cancers, than if you scored in or closer to the healthy range.  That is not to say that everyone else who weighs less than you is healthier, simply that your personal risks are lowered by being closer to or in the healthy range.  See BMI as a benchmark for yourself that you want to work towards (or maintain) the healthy range.

We suggest you use the BMI calculation in conjunction with a few other measurements to get a bigger picture of your health & risk factors.

Waist circumference

A waist measurement (at the navel) of 88m for men & 80cm for women puts you in the highest risk category for chronic disease. Working towards reducing this gradually overtime, drastically improves your health outcomes.

There are some simple ways to achieve this:

• Reduce your sugar intake from processed foods and alcohol (control your blood sugars)
• Do regular strength training (increases metabolism)
• Reduce stress (lowers cortisol/insulin)
• Do regular huff & puff exercise (improves heart & lung health)

Visceral Fat

Visceral fat refers to the amount of fat your body has stored in and around your organs and diaphragm.  It goes hard and puts pressure on your heart & lungs.  Someone can appear outwardly “thin” and still have high levels of visceral fat. This is usually the result of poor diet, so the best thing to do to improve it is to eat more fresh fruit & vegetables and reduce then cut out processed foods, refined sugars, soft drink and junk.

We use these bio-impedance scales to determine Visceral Fat, these send a low current through the body and use a formula to determine a rating.

Body Fat %

As an overall portion of your body, generally speaking we want to have lower body fat %.  The healthy ranges are different for men & women, as women hold fat in breast tissue and need higher levels of body fat to maintain hormonal balance and reproductive health.  There are 3 main readily available ways to determine your body fat %: skin folds using callipers; using bio-impedance scales; having a DEXA scan.  For our clients we use bio-impedance scales because it is less invasive than skin folds and way cheaper than a DEXA scan.

As part of your overall health data, these 4 metrics give you good information to work with.  If you are sitting in the overweight category, and you also have a high waist circumference, body fat % or visceral fat, this verifies BMI the result.  If you have average results in these other metrics, then it tells you BMI is less relevant for your body right now, but good to keep an eye on so it doesn’t creep up if anything else changes.  Remembering the closer you are to healthy range, the less risk you are of chronic disease.

If you have any questions about your BMI please feel free to comment below.