Body Mass Index | What It Is and How to Properly Use and Read It

How to Use The BMI Calculator in Relation To My Body Mass

What is a BMI Calculator?

A BMI (Body Mass Index) score is used to determine the general health of an individual based on their height and weight.  A BMI calculator is a tool that provides you with a score that helps determine risk factors and if you are considered to be healthy or unhealthy.

How is a BMI Score Calculated?

There are many tools available online that will allow you to input your specific data to get your body mass index score.  Each score is categorized is one of the following classifications:

• Underweight
• Healthy
• Overweight
• Obese

Such tools generally will look for two key data points for you to enter and can be calculated using two different measurement units (Imperial and Metric).

The Centers for Disease Control and Prevention (CDC) has two formulas you can use to calculate your body mass index yourself if you preferred to do so without the use of an online BMI calculator tool.  Below you will find the two formulas based off of the unit of measurement you prefer.

When it comes to gender, the formulas found above, as well as a BMI calculator tool found online, makes no difference.  Both men and women (as well as children – but interpreted differently for them) are able to use the formula or online BMI calculator tool to determine their own body mass index score.

Note: Due to children constantly growing, they may use the BMI calculator but it would be best to follow the guidelines set by your doctor when determining their overall health and risk of disease and/or illness.

What’s great about using a BMI calculator is simple – it’s fast and inexpensive.  Sure, you could go get your body fat analyzed using something like body fat calipers or a handheld bioelectrical impedance device by your doctor or certified professional at your local gym, or go a more expensive route by using underwater weighing or dual-energy x-ray Absorptiometry (DXA) – but that takes time and money.

If you want a quick overview of your health as it relates to your height and weight which is still fairly accurate (will determine if you’re in a healthy range or underweight/overweight/obese), a BMI calculator can give you the information you’re looking for.

Does BMI Actually Matter?

Absolutely.  However, there is one group where the results can be skewed (we will touch on that in the next section).  For the majority of individuals, the results from a BMI calculator can prove to be extremely accurate.

According to the CDC, using a BMI calculator and analyzing the score results can be extremely useful in determining the relationship between body fatness and the risk of disease and metabolic problems according to research published^1,2,3,4,5,6.

One Measurement and Classification (Flaw) Not Taken into Consideration

As mentioned in the section above, there is one group where the BMI score can be skewed and not be a good representation of an individual’s overall health and weight (body fat).  That group would be athletes or those who are extremely fit.  Why is that?  It’s because BMI, unfortunately, ONLY considers weight and height in its formula and calculation.  This does not put into account lean body mass and how much muscle someone may have.

Bodybuilders are a good example of how a BMI calculator can provide an invalid look at the individual’s overall health and risk factors.  You could have a 250-pound professional bodybuilder who is 5’8” and scores a 38.0 for their body mass index.  According to their score, that would classify them as being severely obese.  Now, if you’ve ever seen a professional bodybuilder, they are generally incredibly lean with visible abs and when competing are well under 10% body fat.

With all that being said, if you are an athlete and carry a good amount of lean muscle mass, it would be recommended that you utilize one of the other means of viewing your body fat (calipers, bioelectrical impedance, underwater weighing, or dual-energy x-ray Absorptiometry) and how that number relates to your overall health and risk of illness and/or disease.

What Should an Adult BMI Be?

Using the formulas found above or an online BMI calculator, input your specific data to figure out your BMI score.  From there, use the chart below to determine what classification your score puts you in.  You should strive to be in the “Healthy Weight Classification” which would be a BMI score between 18.5 and 24.9.

If you find you are below the healthy classification, you should strive to focus on adding some healthy body weight as you are considered “underweight.”  If you find you are above the healthy classification, you should focus on losing body weight by concentrating and putting more emphasis on your nutrition and exercise.

Sources:

¹Steinberger, J. et al., 2005. Comparison of body fatness measurements by BMI and skinfolds vs dual energy X-ray absorptiometry and their relation to cardiovascular risk factors in adolescents. Int. J. Obes., 29(11), pp.1346–1352.

²Sun, Q. et al., 2010. Comparison of dual-energy x-ray absorptiometric and anthropometric measures of adiposity in relation to adiposity-related biologic factors. Am. J. Epidemiol., 172(12), pp.1442–1454.

³Lawlor, D.A. et al., 2010. Association between general and central adiposity in childhood, and change in these, with cardiovascular risk factors in adolescence: prospective cohort study. BMJ, 341, p.c6224.

⁴Flegal, K.M. & Graubard, B.I., 2009. Estimates of excess deaths associated with body mass index and other anthropometric variables. Am. J. Clin. Nutr., 89(4), pp.1213–1219.

⁵Freedman, D.S. et al., 2009. Relation of body mass index and skinfold thicknesses to cardiovascular disease risk factors in children: the Bogalusa Heart Study. Am. J. Clin. Nutr., 90(1), pp.210–216.

⁶Willett, K. et al., 2006. Comparison of bioelectrical impedance and BMI in predicting obesity-related medical conditions. Obes. (Silver Spring), 14(3), pp.480–490