A scale that can tell you 12 things looks fancier than one that can only tell you one or two metrics, right? Smart scales are marketed largely by the number of features they have. Even though I have more muscle than the average person my size, the numbers get even less realistic for me with athlete mode.) What about all the other numbers? (And yes, I’ve tried turning on “athlete” mode. My Withings smart scale has never showed any meaningful change in these numbers for me, even when I know my body composition has changed. Some people say they like to watch their body fat (or muscle mass) change over time, and that it goes in the direction they’d expect. If you truly want a number, any number, a simple calculation like the Navy body fat estimator is probably going to be just as good.

That’s not really accurate enough to know for sure what your body fat percentage is. It can also be thrown off by how hydrated you are, how recently you have exercised, and whether you have artificial knees or hips.Ī review article on the accuracy of BIA points out that, because so many assumptions are required, even the best devices and algorithms are probably never going to be able to give totally accurate, detailed body composition information for an individual:Ī fundamental problem is that BIA is a predictive method that inherently requires simplifications and assumptions based on population mean values yet considered as being accurately applicable to all subjects.Ī Consumer Reports study from 2016 found that the scales they tested differed from a BodPod measurement of body fat by anywhere from 21% to 34%. The biggest is just the number of guesses the formula has to make about your body to get from “this is a 5’6″ human with a foot-to-foot resistance value of X” to “your body is 32% fat,” much less estimating the amount of bone or dry muscle tissue.įor example, it makes assumptions about how much of your fat, muscle, and so on are in your upper body versus your lower body. And based on the resistance it measures, it comes up with a guess about how much of your body is made of fatty tissues versus watery tissues.Īs you might expect, there are many limitations to this approach. It uses your height (which you enter into the app when you set up a profile) to guess at the length of this horseshoe shape. In essence, the formula imagines your legs and hips as a sort of horseshoe shape made of a mixture of water and not-water. The scale can detect the electrical resistance between one foot and the other, which means the current is running up one leg, through your torso, and down the other leg.

Us navy body fat calculator accuracy