It really depends on how you do them. speed, effort, etc... Exactly, like it's described in here: "As an example, let's consider our hypothetical 165-pound person again. When they resistance train moderately for thirty minutes, they can expect to burn about 112 calories. If, however, they resistance train vigorously for that same thirty minutes then their caloric burn will climb to 225. Again, the result more than doubles because the user has put in more effort." - from ArticleBase. You can measure your personal number of calorie burn per hour while ab crunching with a heart rate monitor. These, according to weight, height and sex input will give a pretty accurate result. Good luck.
