The number of calories burned doing 100 crunches is small; the movement of crunches is so minimal that people don't burn many calories doing them. While crunches are effective for strengthening muscles, they are not cardiovascular exercises, which burn the most calories.
The number of calories burned with activities varies depending on how much a person weighs. In order to get the abdominal muscles they want, people need to incorporate both crunches and a cardio exercise into their routines. A cardio exercise is one that gets the heart to pump faster than normal.
A person who weighs 200 pounds and in-line skates for an hour can burn 683 calories, according to Mayo Clinic. A person who weighs 200 pounds and walks for exercise can burn 255 calories an hour walking at a slow pace.