So, How Do You Calculate BMI (Or Body Mass Index)?

First off, here’s a look at the simple BMI calculator I use. Plug your age, sex, height and weight in and press ‘Calculate’.

BMI Calculator For Adults, Children And Teenagers (Ages 2 And Up)

OK, So What Is A Healthy BMI? (Adults First)

The table below details the full range of BMI scores and how they are classified for adults and as recommended by the World Health Organization (WHO).

BMI Table For Adults (Aged 20 And Over)

What Should My BMI Be And What Does It Mean?

As you cannot alter your height, the BMI is in essence a measure of your weight, and whether it is normal, or whether you are underweight or overweight.

As such, it is a good indicator of the amount of body fat levels for most people. You ideally would want to be falling somewhere within the normal range.

Overweight and obese BMI values are related to a higher risk of some diseases and conditions including:

• Heart disease
• Stroke
• Certain cancers including breast, colon and endometrial
• Osteoarthritis
• Type 2 Diabetes
• Sleep apnea and respiratory problems

BMI is a good indicator of body fat levels but it is not perfect. Women do tend to carry more fat than men and the older the get the more fat you have. More on the BMI differences between men and women below.

You can consider additional factors when considering the likelihood of disease, but BMI is a very good indicator and a good starting point for most of us.

How To Calculate BMI Manually

So, how do you calculate BMI manually? The Body Mass Index forumula was originally devised by a 19th century statistician from Belgium who went by the name of Adolphe Quetelet.

I’ve listed his formula in two forms, firstly in imperial, then in metric, units.

BMI (lbs/in²) = (weight in pounds x 703) / height in inches²

BMI (kg/m²) = weight in kilograms / height in meters²

Alternatively, you can just check your weight and height on the BMI table below and you’ve got your answer.

BMI Index Chart For Men And Women (Aged 20 And Over)

How To Calculate BMI For Women And How To Calculate BMI For Men? There’s No Difference!

Well, there isn’t according to the World Health Organization (WHO) anyway, or other leading health institutions like the Centers for Disease Control and Prevention (CDC) in the US.

Ok, the BMI calculator on this page has a male and female option to choose from, but in fact you’ll notice that the results come back just the same whichever sex you choose for adults. Results will differ for children though (up to 20 years old). More on this later.

On average, women tend to carry more fat than men, although men carry more muscle, which weighs more than fat. As a result, after the age of 18 men come back with slightly higher BMI values than women.

Based on these findings, the thresholds for being overweight and underweight should perhaps differ slightly between men and women. The argument would be that the overweight threshold for men should be somewhat higher than for women.

There is also uncertainty around maintaining only one BMI classification for all ethnic groups, as for example some Asian and Pacific communities might be more prone to the risk of diabetes at lower BMI levels.

WHO has decided for now to stick with a single classification across men and women and across ethnic groups, partly because some of the evidence to modify things is conflicting, and partly I suspect so that BMI remains a simple to use and simple to interpret measure.

The National Health Service (NHS) in the UK though has gone further and recommends that people of South Asian origin should consider themselves at a higher risk of health problems with a BMI of 23 rather than 25.

If you are asking yourself how to figure out your BMI and what it means, you want something simple and I for one want to use it as just one of several broad indicators to tell me if my weight is ok, or if I need to do something about it. Nonetheless, I would always err of the side of caution along the lines of the NHS guidance if this relates to you.

How To Calculate BMI For Children (Aged 2 To 20)

If you are trying to find a BMI calculator for teenage girls or boys, or younger children, there is an alternative BMI classification that applies to everyone aged from 2 to 20.

Whereas the BMI for adults is the same for men and women, and across all ages, normal, overweight and underweight classifications for children vary dependent on age and sex.

This is because BMI is very clearly dependent on the age of the child and the sex. So, how do you calculate your BMI in this case? The exact same BMI formula (using the calculator on this page) is used to work out the BMI, and in fact it will also output a message to tell you whether a child has a healthy weight or not.

However, if you only have the BMI value, the following extra steps are needed for children and teens.

Step 1: Determine Which Percentile The Child Or Teen Is On

Below are links to pdfs of CDC growth charts for boys and girls:

BMI Chart For Boys
BMI Chart For Girls

They show which percentile a child is on depending on their age and BMI score. Knowing the percentile tells you what % of people have a lower BMI than the child in question. In effect, the percentile tells you where you are relative to everyone else.

So, if a child was on the 20th percentile, 20% of children would have a BMI lower than that child, and 80% would have a higher BMI.

CDC has also created a sample chart, shown below, to help you work through the process of determining the percentile once you have the BMI value and age.

CDC Sample Chart

Step 2: Determine What Percentile Relates To What Weight Classification

Now you need to check which weight category the percentile falls into. The table below tells us that.

BMI Table For Children And Teenagers (Aged 2 to 20)

Although BMI is used as a screening tool for underweight, overweight and obesity, it is important to say that it isn’t used to provide a definite diagnosis. It might be the case that a child is heavier but further tests are required to know for sure if that means the child has excess fat.

Only then would a treatment plan be put in place that takes in to account health factors and that might involve counselling and changes to diet and exercise for example.

What Next?

So, you know how to calculate your BMI, and what it means.

When I first checked my BMI, I came up overweight and it gave me a bit of a shock. I thought I was carrying a few extra pounds round the middle but nothing to worry about.

Being officially described as ‘overweight’ gave me a bit of a kick start though. And I got a MUCH BIGGER kick to do something when I read up on the increased health risks associated with it. I guess I sort of new about some of them, but going through the process here made everything feel a lot more real.

For me, it got me motivated to concentrate on improving my diet and exercising more. For others, the issues may well be more complex, but for many of us exercising a little bit more, to whatever level, will be key to being called ‘NORMAL’ again, at least as far as weight is concerned.

How ‘Find Me A Workout.com’ Might Be Able To Help

OK, I know, the name of the website makes it pretty obvious.

But just to explain a little bit, I’ve tried to put a website together here to honestly review some of the best workouts and fitness programs I can find. For me, it’s important that they’re not only effective but fun and varied too so I can stay motivated to keep going at it.

Otherwise, it’s just another false dawn and I’m back to square one.

I try all the workouts and programs I review so they are real and include my sincere opinions about them.

If you want to check out some of the best I’ve found, please check out the links from the home page.

Whatever route you go down, I hope this article helped you but please let me know if you’ve any comments about your experiences, or queries you’d like me to look at.

Thanks for reading,

Stefan

References:

Centres for Disease Control And Prevention – http://www.cdc.gov/healthyweight/assessing/index.html
National Health Service – http://www.nhs.uk/Livewell/loseweight/Pages/BodyMassIndex.aspx
World Health Organization Global Database on Body Mass Index – http://apps.who.int/bmi/index.jsp