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How to calculate and measure your BMI (body mass index)

Body Mass Index can only be a rough guide to a healthy weight.

May 5, 2019 |
2 min read

Need to calculate your BMI but not sure how to do it? Maybe you have heard the term ‘BMI’ referred to but are not sure what it is? Then we are here with the answers! Here you will find out exactly how to calculate your BMI as well as a lot of other essential information about this method of weight calculation.

What is BMI?

Your BMI (Body Mass Index) is a measure that is used to work out if you are a healthy weight. It is used by doctors, hospitals, fitness instructors and just about anyone that is involved with health and fitness.

The BMI calculation is worked out by taking your weight in kilograms and then dividing it by your height in metres squared. So, if you weight 85 kgs and your height is 69 inches, do this:

  1. Divide your height in inches by 39.4 to get hour height in metres i.e. 69/39.4 equals 1.75 metres. Square this by multiplying 1.75 by 1.75 to give 3.06m
  2. Divide your weight of 85 kg by your height in squared metres of 3.06m which gives 27.7

How do you know if you have a good BMI?

BMI can only be a rough guide to a healthy weight. Various people have different frames and skeletal bone structure so do take this into account. The general opinion is that for an adult aged between 18 to 65, a BMI somewhere between 18.5 to 24.9 is the normal range. For young people and children, a BMI can only be reliable if it also takes account of their age and gender.

Here is the general Body Mass Index guide

Under 18.5 – underweight

18.5 – 24.9 – healthy

25 – 29.9 – overweight

30 – 39.9 – obese

Can the BMI calculation be used for everyone?

No. The calculation will not be accurate for athletes, body builders, pregnant women, the elderly or the very young. This is because the calculation is not refined enough to know whether weight being carried is in the form of fat, muscle or a baby! Athletes will have a higher BMI due to muscle mass.

Children and the elderly will have a low BMI due to not having grown fully or losing muscle mass as they get older. During pregnancy, not only is a woman carrying baby-weight but her body changes massively so BMI will not work.

What do I do if my Body Mass Index is not healthy?

BMI is only one way of measuring whether or not you are at a healthy weight according to your height. Think of it as an indicator and not a figure set in stone. It may not always be the best way to measure your weight as there can be so many other things to consider.

Use it as a guide only and if you feel that you are under or overweight, see your GP and ask him to weigh you and discuss whether you need to change your diet or lifestyle.

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