Q: im around 146 lbs and i was wondering how many calories i burn if i do 300 sit-ups a day and i eat less than 1500 calories a day?

A: 300 situps a day won't burn a whole lot of calories, but more importantly your overall approach to losing weight (I assume that's what you are trying to do) is not the best one. Keep in mind, that just because situps target abdominal muscles does NOT mean that they'll specifically burn abdominal fat. Instead of just doing situps, you need to exercise all your muscles (situps exercise maybe 15% of them) to maximize your fat burning potential. Please read my fat loss article.