Like many first-generation devices, the Google Pixel Watch has many quirks. So far, early users have reported that the watch dramatically overreported calorie burn due to a bug. According to android police, the Pixel Watch team is aware of the issue and suggests that restarting the device may fix the problem. That said, it’s a striking reminder that calorie burn isn’t a reliable measure.
In the case of the Pixel Watch, the bug appears to have affected how a user’s basal metabolic rate was calculated. Basal metabolism, or BMR, is essentially the number of calories you burn each day, simply existing. It is calculated based on factors such as your age, weight, gender and height. If you enter the wrong data, you will get the wrong calorie burn. According to android policeFitbit’s software started with incorrect user data, which was then rectified when the device was rebooted.
That’s annoying, but in the end it’s not that serious. That’s because you should never trust each portable device to give you accurate calorie burn.
You should never trust each portable device to give you accurate calorie burn
For starters, no two wearable manufacturers use the same algorithm to determine how many calories you burn while exercising. They each use proprietary algorithms that take into account factors such as heart rate, accelerometer data, and your BMR. Different workouts will work different muscle groups, which also affects calorie burn – hence these devices have multiple sport profiles for activity tracking. For example, while running and cycling are both great for cardio, you burn a little more while running because it uses more muscle.
There are also dozens of other factors that smartwatches don’t take into account. Taking myself as an example, I have polycystic ovarian syndrome. Burning people with this condition an average of 400 calories less per day than those who don’t. Nowhere on my smartwatch can I tick a box so that the algorithm can take that into account. My smartwatch also doesn’t know how much muscle mass I have, my condition, the medicines I take or the thermal effect of the food I eat.
In short, many people will never get an “accurate” number, no matter how diligently they record their exercise and food. At best, calorie burn via wearables can only provide a broad picture of your long-term progress and activity levels — or a warning that something isn’t quite right. To drive the point home, a Stanford Study 2017 found that of the seven trackers tested, none provided calorie burn stats “that were within acceptable ranges in any environment.” The most accurate had an error rate of about 27 percent. The worst had a 93 percent error rate.
This is the main reason why, as a wearables reviewer, I choose not to evaluate how “accurate” a device’s calorie burn is. I can not do it. At least not in a meaningful way. What I can do – and what users need to do – is check that the stats they’re getting, including calorie burn, are consistent.
While testing the Pixel Watch, I ran three 30-minute runs on the same route, at about the same speed, using the Apple Watch Ultra and the Runkeeper app as controls. The results are shown in the following table.
They’re all in about the same range. I have no idea which one is the right number, but it doesn’t matter as long as they all give consistent results. Which they are. If I wanted to, based on these results, I could use the Pixel Watch to get a rough idea of whether I’m in a calorie deficit or surplus, depending on my goals. In general, as long as two devices are within about 1,000 steps and 500 kcal of your total daily count, you won’t get an arguably different experience.
Now, if the Pixel Watch had given me three completely different calorie burn numbers for the same activities, That would be a problem. At that point, I’d dig a little deeper. For example, when I Samsung Galaxy Watch Active 2, it recorded a walk that was about 11,000 steps and six miles away compared to my control device. Other times it produced results that weren’t too far off. That kind of discrepancy is a red flag.
Of course it would be nice to have a gadget that is 100 percent accurate. It’s also impossible, no matter what a tech executive says at a launch event. Wearables are designed to help you establish your baseline so you can visualize your progress over a longer period of time. If you focus on one statistic — especially one as indirect as calorie burning — you’re losing the woods for the trees.
