Measuring BMI for adults, teen, and children

By Alex Woodrow | Weight Loss

Sep 29

By definition, Body mass index (BMI) is a measure of one’s weight divided by the square of their height. As it is, Body Mass Index mirrors a person’s overall health. The index is more of an indicator than a measurement of your body fat. In simple terms, as your Body Mass Index increases, so does your body fat. The converse is also true.

Check you Body Mass Index (BMI)

Your BMI is

How to compute your BMI

Calculating your Body Mass Index is pretty straightforward. There’s a formula for the same; weight (KGs)/ height (M2). If you don’t love calculations, there are ready-built online tools to help you with the BMI computation. Either way, you should be able to get some BMI value.

Body Mass Index ranges and related health conditions

According to the World Health Organization, the Body Mass Index value can be used to gauge an adult person’s health status. For instance, a healthy individual has BMI ranging from 18.5 to 24.9.

Underweights have Body Mass Index values below 18.5. Those who are overweight have body mass index ranging between 25 and 29.9. An adult with a BMI value of 30 or higher is considered obese.

Your BMI value is an indication of your health status. For instance, being obese comes with loads of health conditions. The same is true for overweights. There’s a close link between excessive weight and chronic health conditions such as hypertension, diabetes, congestive heart failure, diabetes, etc. On the other hand, being underweight also poses some other health problems like osteoporosis, malnutrition, anemia, etc.

Exceptions to the rule

Body Mass Index mirrors your health. However, it isn’t the best for measuring certain aspects of an individual’s health.

For instance, contrary to popular belief, Body Mass Index cannot be used to measure the proportion of body fat. However, there’s some close correlation between the amount of body fat and the Body Mass Index value.

Also, BMI cannot be used to tell one’s age, gender, ethnicity, or place of origin or even muscle mass.

All that notwithstanding, if done accurately, Body Mass Index measurement can be used by health professionals to keep track of a person’s weight visa is potential health risks. As such, Body Mass Index is such an important statistic in as far as a person’s health is concerned.

Measurement of Body Mass Index in Adults, Teens, and Children.

What’s the real difference?

As far as measuring the BMI goes, the formula is the same irrespective of the person’s age. That is to say, the method for calculating Body Mass Index in adults, teens, and children is very much the same, except for a few differences. The formula for the measurement of Body Mass Index entails dividing a person’s weight (in kilograms) by the square of their heights (in meter squared). And this formula applies for both adults and children.The SI units for BMI is Kg/M2.

The main difference comes in the interpretation of Body Mass Index values. It is different across the board – for adults, teens, and children. That said, let’s get started with Body Mass Index measurement in each category of persons.

Calculating Body Mass Index in adults

As aforementioned, an adult person’s BMI can be used to tell so much about their health status. There are several methods for computing BMI. Apart from the conventional formula method, you either use the Body Mass Index chart or the BMI calculator.

And as mentioned before, Body Mass Index measurement takes into consideration two main parameters – a person’s weight and height.

  • Using metric units for calculation

The formula for calculating the body mass index is,

BMI = weight (kg)/ height squared (m2)

The standard units for measuring Body Mass Index are as indicated above; kilograms for weight and meters squared for height. You need to convert you’re your measurement units to the standard values mentioned above. In so far as using metric units for measuring weight and height values are concerned, that much is clear.

  • Using imperial units for calculation

Then there is the other option of using imperial units to measure Body Mass Index. If you choose to use imperial units instead of the usual metric units for computing Body Mass Index, the formula is as follows:

BMI = weight (lbs) × 703/height squared (in2)

Using imperial units to calculate Body Mass Index entails multiplying the person’s weight in pounds (lbs) by the quotient of 703 divided by the square of height squared (in2). Remember to measure height in inches if this formula is to apply satisfactorily. If done correctly, the values should be similar to those for the metric units.

That is for those who love using complex mathematical formulae. Count me out! I don’t like complicated mathematical formulae. Technology has made things much easier these days. You can compute your Body Mass Index in an instant. No need to worry yourself with complicated calculations. In that spirit, let me introduce you to two rather contemporary methods of measuring Body Mass Index:

  • BMI calculator
  • BMI chart
  • About the Body Mass Index (bmi) calculator

As the name suggests, this calculator makes it a lot easier to compute BMI values. BMI calculators are available in different brands and models. All of them support both metric and imperial BMI computation. All you need to do is type in the metric or imperial units. The  BMI calculator will do the rest.

  • About the Body Mass Index (BMI) charts

Asides the calculator, you can also use Body Mass Index charts. Using these charts is very easy.  It is mainly about comparing values. In the BMI chart, you are required to look up your height in inches then match the same with a corresponding weight value in pounds.

The BMI is that value at the intersection of your height and weight values from the table.

The beauty of using a Body Mass Index (BMI) chart is that you even get to tell what potential health risks associated with your Body Mass Index value. All that statistic is available at the top of the Body Mass Index chart. It makes it much easier to tell if you are in the normal healthy weight range, underweight, overweight, or obese. You don’t get all that info from the BMI calculator.

Understanding the BMI results for adults

Measuring and interpreting BMI values are two different things. Irrespective of the method used, the Body Mass Index value for adults can be classified and explained as follows:

BMI Weight status
Below 18.5 Underweight
18.5 – 24.9 Healthy
25.0 – 29.9 Overweight
30.0 and above Obese

Interpreting the BMI

  • BMI Below 18.5

When your BMI is less than 18.5, it means that you are underweight. It could be the result of poor nutrition or an underlying health condition. In the literal sense, it means your weight isn’t proportionate to your height. Of course, being underweight can have very dire health implications. You should take the necessary steps to add weight. You should also consider seeing a dietitian or physician for that matter.

  • BMI between 18.5 and 24.9

If your Body Mass Index value is between 18.5 and 24.9, you have every reason to be happy. You are within the healthy range. Call it the comfort zone. Whatever it is that has brought you that, keep at it. In the literal sense, Body Mass Index values in this range imply that the person’s weight is commensurate with their height. However, you must take steps to maintain that status.

  • BMI between 25.0 and 29.9

If your BMI is in this range, you have every reason to worry. You are overweight. It is attributable to different causes. Whatever the cause, you need to do something to lose weight. Eat healthy and workout quite often.

  • BMI above 30

If your Body Mass Index is 30+, you are excessively overweight. You are obese. There are many reasons for this. It could be genetic, some health conditions, unhealthy eating habits, or a sedentary lifestyle. Whatever the reason, you should strive hard to reduce that weight. Check what you eat and workout more often. Contact your physician and workout coach for further advice.

Calculating BMI for Teens and Children

Notice that the Body Mass Index computation for adults, teens, and children uses the same formula. However, we didn’t consider age and gender in the adult BMI calculations.

For teens and children Body Mass Index’s however, we’ll consider age and gender. However, there’s not much emphasis on the child’s weight because:

  • Males and females have different body physique that changes at different rates in either sex.
  • Weight values may differ significantly every month
  • The weight values change with the height of the child.

As such, for more accurate interpretation of BMI values for teens and children, it is recommended to use a Body Mass Index-for-age chart for children and teens in line with the child’s gender.

BMI calculator and charts for teens and children

The Centres for Disease Control and Prevention (CDC) has a BMI calculator for teens and children. Also, there’s the CDC growth chart with corresponding BMI-for-age percentiles for children and teens. Be sure to use the Body Mass Index chart to evaluate and interpret the child’s Body Mass Index values.

Interpretation of the BMI-percentiles chart.

The table below gives a better explanation of the results

Weight status category Percentile range
Underweight Below the 5th percentile
Healthy weight Between the 5th percentile and the 85th percentile
Overweight Between the 85th percentile and less than the 95th percentile
Obese Equal to or greater than the 95th percentile

Why doctors need your BMI?

By design and function, BMI is not a diagnostic tool for the simple reason it is not accurate. However, it is handy in screening for likely weight problems in children and adults alike.

When a patient presents with an abnormal Body Mass Index, doctors usually go further to assess other related aspects:

  • The patient’s diet and lifestyle
  • Family history of cardiovascular problems and other health-related complications
  • Skinfold thickness (which would determine the amount of fat in the body)

After the assessment, the doctor will recommend the necessary steps and precautions to take. The measures range from dietary changes to lifestyle adjustments.

Health risks associated with excessive weight

If your BMI (Body Mass Index) value measures 30+, then you are obese. There are several health risks associated with excessive weight. Some of these include:

  • Hypertension
  • High blood cholesterol and triglycerides levels
  • Low levels of High-Density Lipoproteins (HDL) – good cholesterol – in blood.
  • Risk of type II diabetes mellitus.
  • Risk of cardiovascular diseases.

Bottom-line on Body Mass Index (BMI) measurements

To stay healthy, you need to do routine BMI checks. That is the best way to stay healthy and ward off potential health risks. Eat healthily, work out regularly, and consult your doctor regularly. That’s all you need to do to keep your BMI within the healthy range.

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About the Author

Alex Woodrow has been a contributor for for over 10 years and has a deep passion for Male health and well being. Alex has studied chemistry at UCLA and has a thorough understanding of the supplements industry, product formulation and the science behind male health.

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