There is a difference bweeten reps and time. You might be doing them really slow or really fast. If the total workout equals more than 30 minutes then, yes, it is good. If it is less then it is still good for your health but perhaps not enough. It doesn't matter if you don't do them in a row. Just do 10 minute bursts when you have time 4 times a day or something. Whatever works for you. As for the calories, it depends on the time you do it and your weight, just look up calorie burned calculator jump rope' on google and you should find one.