I've seen a lot of calorie measurements in the forums that are really ridiculous, all the way from 800 calories per hour (possible, but not likely) to 1,600 calories per hour.

Looking at Juan Antonio Flecha's power meter statistics helps put things in perspective.

Flecha's Functional Threshold Power (FTP, or the average power a rider can produce for 1 hour without fatiguing) is a massive 420 watts. The average young male novice cyclist in reasonably good condition has an FTP of 200 to 230 watts.

With this in mind, look at Flecha's calorie consumption in the TDF in the first 9 stages: 34,569 calories in 39 hours and 2 minutes, for an average of 886 calories per hour. That means if you are a young novice male in reasonably good shape, your calorie consumption per hour is likely to be around half of Flecha's, or 443 calories per hour.

The calorie consumption per mile is even more sobering: 989 miles in 9 stages, which equals 35 calories per mile. So, if you can produce the power output of a Flecha, then you can reasonably claim you burned 350 calories in your 10 mile ride. But if you're a clydesdale like me, 20 to 25 calories per mile is about the best you'll do, and even that's only if you're pushing it pretty hard.