Q: how many calories do you burn while doing sit ups?

A: Very few, and it doesn't really matter. Sit ups are just one exercise that targets only a small part of your entire muscle mass. Situps are maybe 5% of what a good complete fat-loss program should be. So don't worry about situps or any one other exercise and instead focus on have a good overall program, including a fat-burning diet and heavy whole-body weight training. Please read my fat-loss article and follow its directions. Good luck!