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The Samsung Galaxy Watch 4 has a sensor not seen in smartwatches before. It’s the Body Composition sensor.
This is arguably more useful than the Fitbit Sense’s EDA stress sensor, the blood oxygen feature of countless wearables, or even the ECG of the Apple Watch Series 6 and Galaxy Watch 3. That last one may save your life, but you can use the Galaxy Watch 4’s Body Composition as a regular motivating factor in your workout routine.
It works much like a body fat analyzer scale.
The Galaxy Watch 4 Body Composition screen
One part of the body connects to the first conductive node on the device, another part the second. In a smart scale, the base of each foot is used. The Galaxy Watch 4 uses the underside of your wrist and two fingers of your other hand.
This completes a circuit of sorts, and the Body Composition hardware then sends a weak electrical impulse through your body. The varying impedances of fat, water, muscle tissue and bone affect the signal as it passes through. Samsung puts this data through an algorithmic grinder and spits out your results.
How you use Body Composition
You access the Body Composition feature in the Samsung Galaxy Watch 4 by swiping a few times from the watch face to access the right “widget” page. Or by turning the bezel on the Classic edition.
You are shown a few explanatory screens, and a warning that the figures are only made as a guide, for entertainment purposes if you like, and that those with a pacemaker should not use Body Composition.
Galaxy Watch 4 Body Composition instructions
The actual process is refreshingly fast. Samsung recommends you first move the Galaxy Watch 4 up to a fleshier part of the wrist. You then place the tips of the ring and index fingers of the other hand onto the side buttons, raise arms away from your body wait for around 20 seconds. This is the data-gathering phase.
The Samsung Galaxy Watch 4 then displays a page of stats. Here’s the list:
- Weight (entered manually)
- Skeletal muscle
- Fat mass
- Body Water
- BMI
- BMR
BMR stands for basal metabolic rate, and indicates the calories your body needs to sustain its current status each day, without accounting for any exercise. Body Composition doesn’t have a hand in all of these stats. BMI is a calculation of weight against height, and you will need a scale to determine your weight.
Galaxy Watch 4 Body Composition results
How accurate is it?
Body fat scales are not particularly accurate. They all generate stats via algorithm, based on limited core data.
After trying the Galaxy Watch 4’s Body Composition feature a half-dozen times, the figures for water and skeletal muscle changed quite dramatically on some runs. However, body fat remained largely consistent.
Galaxy Watch 4 Body Composition results
Hydrostatic weighting is one of the best ways to measure body fat. This compares the weight of a person underwater versus their weight on dry land. It’s accurate but not convenient, and I didn’t have access to such hardware ahead of this write-up.
I did, however, have a chance to compare the Samsung Galaxy Watch 4’s results to those of a consumer-grade body fat analyzer scale from household favourite Salter. Its results were quite different to the watch’s, placing my body fat percentage at 18.1%, to the Galaxy Watch 4’s 22-23.5%. That’s the difference between "fairly OK" for someone without too much muscle mass, to borderline unhealthy.
However, I should note here the test Samsung Galaxy Watch 4 was not linked to my Galaxy Fit profile, so may not have accounted for all of my vitals. And these watches — a couple from the Galaxy Watch 4 family were tested — are likely not running final software.
The same core advice that is sensible to apply to other semi-accurate readings applies here. Samsung’s Body Composition feature is best approached as a relative measure, to check on your progress over weeks, rather than obsessively mapping the results against the charts of desirable body fat results you can find online. It’s a neat stat that adds to the usefulness of fitness watches.