Simple guide to BMI

If you've been hearing the phrase BMI being bandied around a lot lately, but aren't sure exactly what it means or how it affects you, we can help. BMI stands for Body Mass Index, and is a system used to give people an idea of whether or not they are within the "normal" weight range for their age, sex and height.

How does it work?

In order to calculate your BMI, there is a formula that needs to be followed. If you know your weight in kilograms and your height in metres, you need to divide the former by the square of your height. If you know your weight in pounds and your height in inches, and then multiply your weight by 703 and divide by your height in inches. The resulting number will be your BMI rating. (You can save your brain the workout by using bmi-calculator.net to do the hard work for you).

What does this number mean?

The number that you get when you are done working out your BMI needs to be compared to a chart, which will give an indication as to how healthy your weight is. A rating below 18 means that you are classed as underweight, a rating of 18.5 to 24.9 means you fall within the normal weight range for people your sex and height, 25 to 29.9 means that you are overweight and anything above 30 is classed as being obese.

How accurate is this?

The main problem with the BMI system is that it fails to take into consideration a number of different things. For example, if you work out a lot or are athletic, it's possible that you will show up as being overweight or obese even if you clearly aren't. This is due to the fact that BMI does not take into consideration that muscle weighs more than fat.

Sould it be taken seriously?

While some people swear by the BMI system, the fact is that it has too many holes to be considered an accurate measure of anything these days. It is becoming increasingly marginalised by more advanced techniques like measuring body fat percentage these days, and it is likely that it will be come increasingly so in years to come.

However, that's not to say that it should be completely disregarded. It can offer a reasonably accurate idea of just where you stand with your weight, so it can be helpful to use it as a quick reference tool more than anything else.

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