In theory, to lose a pound of fat from your body, you need to use (exercise in excess of your caloric intake) 3500 calories, which would translate into roughly 600 grams of fat.

Of course, it's not that simple since there is always a play on what fuel source is being used, meal timing, etc.

The best guideline I saw (I'll see if I can dig up the article/study) was that if your goal is to lose bodyfat, daily aerobic activity of 45 minutes is KEY, along with calorie control and weight training/resistamce training so that each muscle group gets hit AT LEAST once per week.