What is your experience with calorie calculations...do you find it credible (bike)?

Honestly, 1681 calories for a 2hr ride @ 12 mph sounds like a huge overestimate (unless there is some pretty significant climbing involved).

If you want to get reasonable calorie results from heart rate, you need to have a good idea of your true maximum heart rate (and not just the default 220 minus age formula).

I find that my running and biking calories are usually fairly close to what this website reports:

https://caloriesburnedhq.com/

Using that web site calculator, it gives me 1,549 cal. My gut feel is that "this seems a bit high", since my speed is only 11.9mph (for ~2 1/4 hr). But, at any rate, the Fenix gave me only 738 cal for that same data...which seems too low. So, this is my dilemma!

But, if you usually get rough agreement between what the Fenix gives you and that calculator, do you (or anybody) have a theory on why the Fenix would give me a calorie figure that differed so greatly from the calculator?

Interesting stuff. Thank you for replying!

Were you using a chest HRM? If you used the F5's OHR on your wrist while riding a bike, all bets are off. Any chance you can share your ride?

And next question - setup of the watch: weight, heartrate zones, max heartrate and activity class.

I use a Scosche optical HRM that pairs with my F5. I have found the OHR sensor on the watch does not work well with my small wrist, and if I try to wear the watch higher on my arm it just slips down. So, I can't say as to reported calories with only the watch OHR monitor. As for the huge discrepancy between the website and the F5, I have seen them track maybe within 10%. But the thing is, I look at the calories, mostly, as a relative number. I don't think either the F5 or the website, or anything else, is really going to give you an accurate measurement of calorie burn.

I find that my running and biking calories are usually fairly close to what this website reports:

https://caloriesburnedhq.com/

This website reports some absurd numbers to me.
I entered data for an 80kg rider going for 1 hour @ 25 kph. The result - 1386 Calories, which is impossible. Possibly, the site is confusing calories with joules, as 1386 kJ would be a realistic number.

Riding a race bike on a flat road, such a rider would need to pedal at about 110 watts. This means roughly 380 Calories (as per bikecalculator.com)

Accoring to velopress.com, pro cyclists burn 600-900 Calories per hour during hard training and racing. Clearly, an average person will not be able to burn nearly as much, even if going all-out (which, I assume, you weren't doing).

Based on all this, the 738 you get from Fenix seems pretty spot on.

Note that these are "active" Calories. Some devices report total Calories, which would include the BMR (an additional 200 Cal or so per hour for such rider).

Wow...so many great responses and ideas.

I just shared my ride. I clicked "everyone" on it. I'm not sure how that makes it accessible, but there it is. It is from 11/25/18, called "King County Cycling", if you can find it.

I only use the wrist HR monitor. Somebody remarked "all bets are off". I can imagine that the wrist HR could be not so accurate, off...maybe 10-20% or something? But, getting like 100% variation in calories seems too big. Are calories therefore that far off because of inaccuracy of wrist HRM? And if calories were low this time, are they equally likely to be off on the high side next time? Or is there a general tendency for calories to be off on the low side based on wrist HR?

That leads to a question, does anybody know how the Fenix calculates calories, or if not the exact formula, at least what are the inputs that influence the calculation. HR obviously. What else? Does it use things like average speed, elevation gain/loss?

Active calories vs. total calories. The manual actually says "your calories burned includes your base metabolism plus activity calories." I think most web calculators and web tables report this amount. I have never seen just the "incremental activity calories" isolated out. But, is there some belief that the manual is wrong and just the activity incremental activity calories are reported by the Fenix? This could explain it reporting a much lower number than other sources, if true.
Max HR-- i let the Fenix calculate by default. Looking at it, I see it uses 220-Age. Will it refine that beyond that simple formula? I thought it might do a more sophisticated calculation since it is collecting so much data.

And then, what is the "real answer"? I guess that is the question. I have collected values from some tables around the web and averaged them and adjusted for my weight, and by my computation a 178 lb male, 12mph for 1 hr = 599 cal. But, the Fenix reported 323 per hour. A big difference! A comment above was that highly trained cyclists are burning 600-900/hr. Making my leisurely ride unlikely to be 600! Anybody have thoughts on the "real" answer for calories burned/hr (178lb male, 67yo, 12mph)? Assume flat, no wind, and average on everything else (tire resistance, etc).
Thanks!

Active calories in my answer were referring to the calculated values from speed/weight on bikecalculator.com.
For some reason, I was under the impression that Fenix also reported only "active", since there's a widget on the watch that separates daily "active" calories from the overall number, but apparently I was wrong there. Who ever reads the manuals? :)

I just checked out my yesterday's indoor trainer session....I was pushing quite hard (TrainingPeaks reported 0.90 intensity factor) for an hour (83 TSS), and Fenix says 712 Calories. If that includes BMR (as per manual), the number seems quite realistic.

The Fenix will never adjust your maxHR downward, because it can never know if you ever really tried to measure it. So if you set it too high, it will remain too high, and that will definitely have an effect on calculated calorie burn (underestimating it).

Bottom line, however, is that you can't get a real number outside a lab, where they can measure your O2 consumption and calculate your energy expenditure from that.

Out of all the numbers, I think the one from bikecalculator.com seems most realistic to me. If I try your numbers, I get 331 active calories, add some BMR and you're around 400. Give or take a little based on your fitness level.

This is a bit more than what Fenix reports for you, but:
- if your maxHR is set too high, Fenix will underestimate calories
- wrist HRM tends to be underreported during activities

Those two factors combined could well explain the difference between 400 and the 330 your Fenix gave you.

What is certain is that the 1,681 Calories from your Edge are definitely way too high.

Active calories in my answer were referring to the calculated values from speed/weight on bikecalculator.com.
For some reason, I was under the impression that Fenix also reported only "active", since there's a widget on the watch that separates daily "active" calories from the overall number, but apparently I was wrong there. Who ever reads the manuals? :)

F5 always displays calories as TOTAL calories: i mean every activity app you can use like run, cycle, swim.... any. The only way you can obtain the split between Active and Rest calories is in the Calories widget.

Regards.