Used 935 for 1st time, calories burned during run is grossly inaccurate?

If anything the strava ones are likely grossly inaccurate.

There’s not really much evidence that you can directly relate the calories estimated on the watch to your realistic defininitve output but usually the watch will be more accurate as it will at least take account of how hard you worked by HR as well as weight, speed etc.

How much do you weigh? 496 does seem a little low but I’d only expect around 800 kcal on an easy Run at 85 kg for myself so it could be down to your weight or it could be that the watch is still learning ‘you’

Tom

Let's just say Garmin is very conservative with calculating calories. Do you have your weight set correctly in both GC, and the 935?
And don't forget, the more you run, the more efficiently your body gets. Let's say you are very skinny, and ran those 8.6miles very slowly (9min/mile or even slower), then 500kcal seems about right I'd say.
I don't remember where I read it (I think H. Steffny) but a rule of thumb is 7kcal burned per minute under fat burning slow jogs, and 14kcal/min when you venture into aerobic territory.
At the end of the day though, I wouldn't pay attention to calories at all. As a runner you're at the lower end of a healthy BMI anyway.

An estimate you can use for running on a hard and level surface is 1kcal/kg/km. So for an 62kg runner going 8.6 miles (13.8 km) this would be around 860 kcal or 860 Cal. (62 kg is an estimate for your weight I got by dividing 100 by 1.6).

Interestingly for running the amount of calories required per kilometre does not vary a great deal with speed. So unlike in a car for instance, where there is an exponential increase in fuel consumption as the speed goes up, the number of calories per km for a runner stays pretty constant. Another fun fact is that running slowly is more efficient than walking fast when it comes to energy use.

When I look at my runs on Garmin Connect it shows on average a bit under 70 kcals per km. My weight is 71 kg. I can not see any significant difference in the number of calories on Stava and GC when I compare the two.

As you said this was your first run with the 935 my guess would be that you didn't have your weight set correctly on the watch.

More information:

https://www.brianmac.co.uk/energyexp.htm

What the others wrote: Strava is way off concerning the calorie estimation. Ridiculous. If their values would be reality, I would be half as fat as I am ;-).

Yes, set your parameters correct: weight, activity index, max heart rate etc.

And if I remember correctly, the watch needs some workouts to get to a more precise calculation.

A few possibilities spring to mind:
1. Bodyweight is entered incorrectly (or possibly in the wrong units).
2. HR data is wrong - does the HR data seem reasonable against past experience. If this is your first use of OHR, watch positioning and placement might be wrong, which can give bad HR data. The watch band should be snug, and positioned on the fleshy part of the wrist well away from the wrist bone - this gives it a deeper blood supply to measure, and a better seal against external light.
3. MaxHR is incorrect. If your true maxHR is below the default 220 minus age, the watch may think you are doing an easy run at 60% effort (and not burning many calories), when you are really going at 70% effort and burning more calories.
4. The watch needs to learn your fitness levels. In particular, VO2Max. With a higher VO2Max, you will be burning more calories at any given HR than with a lower VO2Max. It can take a few runs for the watch to assess and adjust to your fitness level. Take a look at your changing VO2Max over the next few runs. In the short term, take a look at the Performance Condition graph on Garmin Connect/GC Mobile from your last run - if it is significantly positive for most of your run, you can expect your VO2Max to increase over your next few runs.

Are you sure about VO2max? I thought it is the other way round. The higher the VO2max is the more efficient you are and burn *less* calories on comparable runs?

While a novice runner may see some gains in mechanical efficiency, for most regular runners, further increases in mechanical efficiency are pretty small.

With a higher VO2Max, you be delivering more oxygen to the muscles for any given heart rate. More oxygen consumed = more calories burned. In this case, I am assuming that the measured VO2Max with the OP's new watch will catch up with his actual VO2Max.

What is your activity class set to in Garmin Connect? A few years back I was messing with some program with my 235. I found if I changed my activity class, my BMR changed affecting the way Garmin calculated calories burned. I found if you do an honest assessment of your class, the calculations are pretty close to what I feel is accurate for me .

higher VO2Max, you be delivering more oxygen to the muscles for any given heart rate

Splitting hairs a little but your VO2max is a measure of the maximum amount of oxygen you can use for an activity. Generally speaking the body can provide much more oxygen to the muscle than can actually be used. You increase your VO2max by developing the ability to convert more if it to energy, usually as a result of increasing capillaries, mitochondria etc. As you get fitter, you require less oxygen for a given pace. So you can either go faster for the same amount of oxygen, or the same pace for a lesser amount.