so after a bit of research and some minor testing of my own I've found that samsung galaxy watch's (every one of them) total calories burned in a day is wildly inaccurate. It's a lot lower than actual calories burned so, if you rely on this information to lose weight (or gain it) like a lot of people do, myself included, then this is not the watch for you.
Let me briefly address the fact that many people are complaining because the calories widget, apparently, is gone. Now I don't know if this is intended by samsung, but that's not very important here since there are ways of knowing that number, first of all the app samsung health still shows this, and also many watchfaces still do that as well. It's probably a sign that they are giving up on measuring the calories. Anyways, as I've mentioned, that number is not accurate so that's even less useful, unless samsung does something about this.
So, this is very simple: some of you may have noticed that if you don't wear your watch for a full day, it still shows a certain number of calories burned at the end of the day (again, you can see this in the samsung health app). It should be around 1500-1900 kcal for most people. That is your basal metabolic rate, that's the number of calories your body needs just to stay alive in 24h.
Your watch estimates that based on your profile (height, weight and so on). In one minute search you can find many calculators on the internet that estimate that number for you, it'll be just as accurate. This doesn't take into account any activity whatsoever, that's why your watch can tell this even if you don't wear it, it doesn't even take into account the calories you burn for digesting what you eat. For the samsung app, it start at 0 at midnight at slowly grows during the day to that number so it makes it SEEM that it's tracking something, but it isn't tracking anything.
Actual calories burned, even if you don't do any particular activity, it's around 30% more than your BMR. Those are the calories you spend to stand straight, to eat, to digest what you eat, to go to the toilet and any other light activity that your samsung watch DOESN'T track.
What your samsung watch does is just adding the calories burned from activities it tracks (or you tell it to track) to your BMR, which is something, but it's still a lot less that all the calories burned in a day from activity your watch doesn't track. For instance, sitting on the couch watching TV or standing straight or cleaining home are still 0 calories for the galaxy watch (it doesn't detect such activity) but those are not 0 calories for your body.
Now, since the watch knows how much I move and what's my heart rate and so on, why samsung doesn't try to make a more accurate estimate of actual calories burned, even outside workouts, is really beyond me. This doesn't seem that hard of an estimate with all this data, even just adding 30% to the BMR would be a more accurate number. This isn't anything new or cutting edge, other brands like apple and fitbit and garmin have been doing it for years. I've had fitbit first, and I assumed all the others worked just like that because it's not rocket science and it just makes sense.