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How Do Body Composition Scales Work?

Digital Scale for measuring weightLike many people I am constantly thinking about weight loss and getting fit. And as a bit of a geek I do like to track my progress. In fact, I find that regular tracking critical. Without it, I’d have a tough time really knowing whether I was really burning that fat or not. One of the more intriguing ways to measure your body fat reduction journey is with a body fat scale, also known as a body composition scale. I was curious for a long time about how accurate these things were, and even how they work. Though they look essentially like a normal bathroom scale, body composition scales will give you a measure of your body fat percentage and other metrics, in addition to your weight. Now that sounds great, but really, how do body composition scales work?

How body composition scales work

Body fat ranges for standard adultsIt’s actually a quite simple, yet interesting mechanism! Essentially, they send a safe, low-power electrical current through the lower half of the body while you stand barefoot on the scale. This electric current will flow faster through water and muscle, and slower through bone and fat. Then with that data included in its programming, the scale measures how fast the current moves through your body, and uses mathematical formulae to give a measure of your body fat percentage.

The great advantages of a body composition scale include convenient, at-home use, and affordability, with many scales weighing in at a price under $100. You’re likely to find some variance among different prices of scales, with the more expensive being somewhat more accurate and having extra memory and calibration features. Other body composition measurement methods, while more accurate than a scale, feature the expense and inconvenience of dunking yourself in a special pool while medical professionals gauge the results. Compared to that, it’s great to just have this little square of metal and plastic that you can stand on anytime and get a reading!

How accurate are body composition scales?

Are body composition scales accurate? That answer is a bit complicated. Consumer reports have found that these scales are far less accurate than other methods of body fat measurement. It turns out that everything from to your level of hydration, the temperature of the room, foot calluses, or even the level of moisture on your feet can all drastically mess with the results. Also, a body composition scale wouldn’t be accurate for children, although you probably wouldn’t want your children  stressing about their self-image anyway.

All of this means that to use a body composition scale in a way that is, well, useful for you, it’s important to be as consistent as possible with its use. Things as simple as having a full bladder or the phases of your menstrual cycle can throw off the results, so you’ll want to weigh yourself at the exact same time of day, with clean, dry feet, and at least be aware of how much you have drunk or ate recently to mentally factor that in.

While the percentage the scale displays isn’t as accurate a measure of your body fat as the more advanced measurement methods, if you’re using the same scale consistently you can use the numbers to track your progress, as your body fat goes down over time. (And hopefully not up!!) I think it’s important also, to not mix different percentage-based fat measuring methods, as the differences in accuracy and scale will tend to throw things off.


In closing, I think body composition scales are an interesting technology, with their use of low-power electricity to measure the contents of your build. While they have problems in terms of accuracy, they can prove  highly useful and motivating in your quest to keep to a healthy diet and exercise regimen for weight loss.  Hopefully you now have a better understanding of how body composition scales work, and can make an informed decision if it’s worth buying one or not.

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