Work out BMI (Body Mass Index)

This article gives a brief about Body Mass Index (BMI), why you need to know it and best websites where you can work out BMI.

What is BMI?

Weight of a person alone cannot determine if the person is overweight or not. It has to be considered in relation to his/her body size, percentage of body fat and so on. Body Mass Index (BMI) is one such simple index or a calculated number which gives an idea of person’s weight with respect to his height.  Body Mass Index is not the most accurate indicator by any means as it doesn’t consider body fat but however it does give a fair picture of whether the person is obese, overweight or underweight. As per its original definition, it is person’s weight divided by square of person’s height. You can work out BMI of your body using one of the links given in the “work out BMI” section of this article below.



Why should I work out my BMI?

As mentioned above it gives a simple and easy picture of whether you are overweight, underweight or obese.  Knowing your BMI will help you know where you stand with respect to average optimal weight for your height and then start devising plans to achieve that optimal weight. Before you jump ahead with any hard core diet plans and/or paid weight loss programs, do understand the limitations of BMI mentioned in the section below.

BMI value and its category

Typically there is a scale which will tell you whether you are underweight, overweight or obese based on your BMI. The most common scale used is listed in the below table.

What is your BMI means?

Category BMI
Severely underweight =< 16.4
Underweight 16.5 – 18.4
Normal 18.5 – 24.9
Overweight 25.0 – 29.9
Obese Class 1 30.0 – 34.9
Obese Class 2 35.0 – 39.9
Obese Class 3 =>  40.0

There are other less common versions of these tables esp. used in Asian countries like Japan and Singapore. If you are from any of these region you might want to refer to them. For more information on those tables please visit Wikipedia link given below.

 

Work out BMI

The formula to calculate BMI is so simple that you can do it using a calculator or on a piece of paper (if your maths is good). However to make life easier there are few good sites which gives an easy interface to enter our weight and height (in any of different units of measure) and work out our BMI. I have listed 3 of the easiest websites which provide a nice interface to work out BMI.

  • nhs.co.uk – Provides a nice and easy way to know our BMI. Takes more inputs than normally required. The interface also provides options to enter details in any of different units.
  • Cdc.gov – This site provides a BMI calculator for children.

Limitations of BMI and things to watch out for

As mentioned before, BMI is not accurate and might not give the full picture of health of person. Hence it is good not to trust this number entirely. This is very much the case esp. if the BMI is calculated for an athlete or an elderly person or young kid. Also irrespective of the number suggested by BMI you also have a fair idea of how good your body is, for example my BMI comes around 26 which put me into overweight category but I am one of the fastest runners in my running club which has a mix of lean and fit blokes. If you are  in any doubt about whether you are overweight or not then its right to consult your doctor or a good dietician for advice. This is a prudent step before you jump into to full fledged dieting just based on your BMI.

 

More on BMI

If you are keen to know more on BMI, the science and history behind it and more below are few links which has very detailed information about various aspects of BMI.

  1. Wikipedia – A site with lot of information about BMI

  2. Centers for disease control – This has information for BMI and information for BMI for children

  3. Healthline.com – Another place to know more about BMI

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