Originally Posted by LMaster

I suspect by three times as long he meant in terms of ride length. In other words, to burn the same number of calories as a ten miler on foot you would need to ride 30. Also from what I've read you would need about 250W for 900 an hour, as the general number if we assume a relatively average metabolic efficiency is around Avg Watt X 3.6 = Calories per hour. On 250W one should be moving pretty quick, probably 21-24 on the flats, and would finish the same 30M ride in around 1:15, giving 1125 kcal, roughly in the ballpark of calories burned from a ten mile run.

At 150W you're probably closer to 19, which gives 540 kcal/hr. In order to get towards that 1100-1200 ballpark you would need two hours of riding, or about 38 miles. So at those wattages you probably need to go 4x the run distance to get the same calorie burn.

Of course, both numbers are lower in the real world since no one rides on a dead flat bike path with no wind everyday. Throw in some wind/hills/stops/etc and you won't have to ride quite as far.