Q: how many calories does 500 crunches burn

A: 500 times more than the calories burned by 1 crunch :) The answer to this question doesn't matter either. You WILL NOT GET FLAT ABS by doing crunches alone! All these crunches will do is build up your abdominal muscles, but they'll still be covered by a thick layer of fat, making them completely invisible and making you look exactly like you do now. This would be the case even if you did 10,000 crunches every day. Just because there are millions of other poor souls trying to crunch their way to six-packs, doesn't mean that you have to make the same mistake. Please fully read and understand this and start following weighttraining and diet programs as explained there.