As a very general estimate, the 100-calorie rule also applies to walking. That is, an average sized person burns about 100 calories when walking a mile. But remember that walking a mile takes much longer than running a mile. So the time it takes to burn 100 calories running is much shorter than the time it takes to burn 100 calories walking. The number of calories you burn while walking will depend on factors such as your body size and your walking pace.