Throughout the day we are constantly burning energy which is measured in the form of calories. Ever wondered exactly how much? The long and the short of it is that we are all different in terms of how our bodies process and use energy. Even if we had two exact same people walking the same distance they may be different based on their movements while they walk. One may swing his arms while the other doesn't.
Good news is that we can try to estimate it and get an average value. As a general rule of thumb you can try using is that you will burn 100 calories per mile for a 160 pound person.
Here is another way of looking at it.
Want to get even more specific? There are many calories burning calculators for free online or available in app form for free.
1)Here is one as a free download from cnet.com
2)Here is an calorie counter app available for android users that tracks how many calories you burn as well as take in. You can get it here
3)Don't want a download? Just want a quick check online? There is a very detailed calculator at NutritonData.com