How Do BMI Machines Work?

Some folks are content to workout and jump on a regular weight scale to measure their body weight. 

And that's great! 

But for those who are very serious about their health care and weight loss, there are additional measurements that can provide more information. A BMI Machine can provide not only your weight but also a rough estimate of the muscle mass versus the body fat measurement in your body.

Smart scales -- like the FitTrack Dara -- can provide up to 17 metrics. 

The performance data that formerly was only available to elite athletes is now available to every body-builder and every mom. 

But how exactly does a smart scale or handheld BMI machine work? 

A BMI machine typically uses an electrical pulse to determine the amount of total body fat. 

These devices send an electrical signal through the body and then read the signal's speed to calculate your water, muscle, and fat levels as the current moves at different rates through each.

See Related: Get Your BMI in 10 Seconds

What Is BMI?


BMI stands for body mass index and takes both your height and weight into consideration when calculating your readout. 

While this does not give you a comprehensive overview of your body composition, it gives you a rough estimate of whether you are at a healthy weight or are potentially at risk for obesity. 


Experts have seen a correlation between BMI levels and other health risks, such as cardiovascular disease and high blood pressure. 


Body Fat Percentage Vs. BMI

So, what is the difference between BMI and body fat percentage, and why does it matter to you? 


As previously stated, BMI is your body mass index and gives you a comprehensive overview of your weight status as compared to your health. 


Body fat percentage, on the other hand, is the amount of fat your body is made up of. 


While there may be a correlation between body mass index and heart disease, many healthcare professionals believe high body fat levels are often one of the risk factors of many health issues like stroke or diabetes. Fat loss and exercise are considered key contributors to maintaining good overall health.


Visceral fat is the most dangerous type of body fat. With the Fit Track Dara, you can check your Visceral fat index every day. 


Are BMI Machines Accurate?

There are good reasons to know and understand both your body fat percentage and BMI. Because people's body mass index has been considered a strong link to obesity and health issues, a handheld BMI machine is a good place to start reducing overall health risks. 


Handheld BIA devices (bioelectrical impedance analysis) are considered relatively accurate. However, they can only estimate your body mass index based on a bioelectrical impedance reading that sends an electrical signal through the only upper body. 


A formula is then used to determine the BMI for the entire body based on the upper body results. 


Calipers can be incredibly accurate when providing these types of readings and are also subject to user error and are often discouraged unless used by someone with extensive experience. 


For these reasons, some people consider a body fat scale to be the most accurate method of reading their BMI.

Alternatives To The BMI Machine (Other Ways To Measure Body Fat)


Smart Scales


Smart scales work similarly to handheld BMI machines, except the electrical current sent up through the electrodes and used to provide a bioelectrical impedance analysis is able to flow through the entire body, not just the upper body. 


Thus the readouts are sometimes considered to be more accurate, as the entire body is measured.


These machines can also provide additional data on your entire body composition. Bone mass, muscle mass, body fat levels, and even total body water can be measured by these machines. 


Helping you to understand your total body weight and how that weight is made up empowers you to better plan your weight loss and health care. 


For example, if your weight goes up, but your muscle mass also increases, you will know that you are actually experiencing fat loss and muscle gain.


With a smart scale, you can also measure hydration levels, which let you optimize your body for peak fitness. 


Skinfold Calipers


Skinfold calipers are an affordable, low tech body fat analyzer. These devices pinch the fat away from the muscle, allowing the user to formulate their body mass index more accurately.


Those who are utilizing calipers will want to take their height into account when determining their BMI. These devices do not give other body composition readouts.



Hydrostatic bodyweight calculates the differences between readouts underwater and online, which allows experts to determine body fat percentage and density. 


Fat is lighter than both and muscle and bone, so the disparity between readings is considered a very accurate way to determine body composition.


Air Displacement Plethysmography

This method works very similarly to the underwater method. This space-looking bod pod measures fat and muscle in the body using air displacement. 


Along with common body composition, readouts like body density and body fat are measured, along with more advanced statistics like energy expenditure and thoracic gas volume. 


This helps medical professionals determine not just weight and BMI, but lung capacity and metabolism rates, useful information for athletes.



The MRI scan can reveal a lot about the body and potential health risks and diagnoses. And it can give you an incredibly accurate reading of your body fat percentage.


 After scanning the patient, medical personnel analyze the results to determine the density of the patient's body fat, ultimately helping them figure out the body's BMI.



Along with reading BMI, fat percentage, and other body composition items, the DEXA test (which stands for dual-energy X-ray absorptiometry) utilizes X-ray technology to determine changes in body density of up to a tiny 1 percent.


 DEXA provides a strong look at bone mineral density, allowing doctors stronger disease control over bone-related risks such as osteoporosis and osteopenia.

How Do Body Fat Scales Increase Weight Loss?

Now that we know all the varying ways to calculate body composition, what can we do with this information? Most will likely put these details to work for their weight loss programs, acting as their trainer and devising a custom health care plan that works for their individual needs. There's plenty of science to show how these products could improve weight loss. For example:

  • The frequency of weighing has been shown to have a direct correlation with increased fat loss and the adoption of healthier dietary habits.
  • Another bonus of daily weigh-ins is the ability to calculate a daily weight average (or even have this done for you in an app with the FitTrack Dara). This helps you cut through the noise of daily fluctuations to provide a more accurate daily weight, increasing motivation as the daily average begins to fall.
  • Smart products read more than just fat percentage and weight. Having consistent access to your body water percentage allows you to catch a decrease in total body water so you can be sure to adjust your habits and keep your hydration up.
  • The visceral fat measurement available through many body fat scales can be a major motivation for overall weight loss and healthier living. Experts have connected high visceral fat levels with other health issues such as cardiovascular diseases, diabetes, or certain types of cancers.
  • Not everyone is interested in weight loss. Some athletes, personal trainers, and people dedicated to healthy lifestyles use body composition scales to help them determine how to best care for their bodies. For example, changes in bone density or muscle mass could be detected and addressed. Similarly, increases in these types of readings are a reassuring sign that an increase in total body weight is for health reasons, rather than an increase in body fat percentage. 
  • Everyone is busy, and smart scales are convenient! Forget trekking all the way to the gym; just step onto your own bathroom scale. Multiple profiles and smartphone compatibility add to the convenience factor, allowing users to store information for multiple family members and access all of their data in one location.