According to All About Abs, doing 100 sit-ups burns 10-15 calories. This estimation considers a 150 pound person performing 30 sit-ups per minute for just over 3 minutes. Increasing the intensity and speed of the sit-ups to 100 in 2 minutes results in the same calorie burn in less time.
Personal weight, diet, general health, activity level and the type of sit-ups performed are all factors contributing to individual calorie burn during exercise. According to ProHealth's online exercise and activity calorie counter, inputting your specific activity, length of activity and current weight yields an estimate of the total calories burned for the listed activity.