I got this formula off the net 3 years ago when I started riding….
I wish I still had the link to post.
Anyway, here is the formula:
A = Cal (or kilocalories) per minute per kilogram = 0.0216 * EXP( 0.144 * )
Total Cal (or kilocalories) = A * Time in minutes * weight in kg
If you want to read the article where I got this formula, I found it here: http://www.frontier.iarc.uaf.edu:8080/~cswingle/misc/exercise.phtml