Originally Posted by
kingsqueak
With HR data it's a wild estimate...without it's more of a guess.
Power + HR is closer, but without metabolic data for the individual still just an estimate.
I look at calories burned as a coarse estimate of effort/output but don't consider it further.
How can having a power meter be anything but near perfect? I mean, it's actually measuring the power you use. That maps to energy pretty darn closely doesn't it?
My PowerTap reports pretty close to what Strava guesses on most rides. Strava can't tell about wind, or my pannier laden commuter bike, but it's great for most road rides.
All others -- Garmin, Ascent, MyFitnessPal -- seem wildly optimistic about how many calories get burned.