An individual doing abdominal crunches can burn as many as 10 calories per minute of exercise. Assuming a rate of 30 crunches per minute, this works out to three crunches per calorie. At that pace, assuming 3,500 calories per pound, it would take over 10,000 crunches to lose a pound.
There are many variables involved in determining how many calories a particular exercise can burn. Some individuals may only burn five calories per minute of exercise, but in any case, doing thousands of abdominal crunches is not the most effective way of losing weight. While sit-ups and crunches can help build abdominal muscles, a regimen of regular exercise, including cardiovascular exercise, along with a healthy diet is a more effective approach to weight loss.