Check out my reply to the calorie thread just below the one you posted.. The numbers you get from endomondo are general averages based on assumptions you provide it, but i'm willing to bet, they're not that far off when you figure in your ride burn + BMR which endomondo probably does.
go to http://www.wolframalpha.com and do a query adjusted for your ride/averages such as
"cycling 180 min, 3.7 min/mi, 36yo male, 5'10", 178lb" (my stats)
and you get:
2440 calories burned
.7 lbs fat burned
128lbs of oxygen consumed
You can also then input windspeed and direction (split your time into two queries, one with headwind or vice versa)
Also, use WOlfram alpha to calculate your BMR so you know what your calorie burn is just being alive.
BMR 36yo male, 5'10", 178lb
Again, these are just averages/assumptions but of all places, WolframAlpha is using the most standard formulas since its the same calculations implemented in mathematica and their built in research tools.
of course none of this includes outside temp, hills, bicycle gearing blah blah blah
