Do you ever wonder how your treadmill knows exactly how many calories you've burned after running a mile? That number you see is comprised of two variables: your weight and your running pace.  The number of calories you burn is basically measuring how much effort it took you to run the mile. A calorie is just a unit of energy and the more you weigh the more energy (or calories) you have to expend when at rest and when running. For example, the average American male weighs approximately 170 pounds and runs approximately a 10 minute mile pace. Researchers have determined that for the “average man,” running burns approximately 125 calories/mile. The formula they use is .75* your weight (in pounds). This information is helpful as a base, “ballpark figure,” but don’t make any important decisions (like whether or not to have another IPA) based on these numbers.

To determine an exact figure for how many calories you burned in a mile, you will have to dust off the human physiology textbook and perform a complicated algorithm; taking into into account the amount of oxygen per kilogram of body weight and multiply that by the duration of exercise you are doing (in minutes). If you are so inclined, the actual equation for calories burned by running (or any other exercise for that matter) is ((METs * 3.5 * weight in kg) / 200) * duration in minutes)).Oxygen consumption is often overlooked, but completely necessary in determining a precise number. Think about it- does Olympian 800 meter runner, Nick Symmonds, average the same energy expenditure as a guy of equal weight who took up running yesterday?

Resources:

Daniels, Jack. Daniel's Running Formula. p.19

Turner, Amanda and Matt Owings, et.al. "Improvement in Running Economy." Journal of Strength and Conditioning Research, 2003, 17(1), 60–67