Originally Posted by
chasm54
Don't assume accuracy. HR monitors use very different algorithms for this, and report widely differing results. If one has a powermeter one can make a reasonably accurate calculation, because it record how many kilojoules are produced and kilojoules divided by four is approximately Calories burned. Those who use powermeters consistently report Calorie consumptions lower than HR monitors alone, in my experience.
I weigh 195lbs. For me to burn 1000 calories in an hour on a flat, windless road I'd need to be riding at close to 25 mph.
And, your error is assuming flat, windless roads. Runkeeper is pretty accurate for myself (I obviously have very average metabolism), as I am losing weight right about on track as I'm supposed to be.
Runkeeper (And Strava) take into account incline and decline, as well as speeds at point in time, rather than average speed for their burn calcs. Runkeeper also uses NOAA data to estimate headwind/tailwind conditions (Strava might, I don't know).
Power meters are about as accurate as it gets (I think), shy of that breathing harness athletes wear to measure calorie burn rate. However, I've found RK (And Strava) to be close enough for the "Everyman" usage (Again, assuming a pretty normal metabolic rate).