Well, you have to burn 3500 calories to lose one pound. And, you should really aim to lose 1-2 pounds a week (sorry, just important to add that, I think). But, you always have to look at the calories you're entering in your body versus taking out. Like, you should consume 500 less calories than you eat at the minimum. For instance, if your BMR is say, 2000 calories, then you would want to aim to consume 1500 calories at the most (this is more important than looking at how many calories you need to burn to lose a pound).
You have to create a deficit of 3500 calories to lose one pound
so if you eat 2000 calories but your body uses up 3000 calories
it will take you 3 1/2 days to lose one pound of weight
That's only half the equation. If you're eating a lot, you can burn any number of calories and not lose an ounce! Losing weight is 3/4 about controlling what you eat, not about burning calories.
Often I hear it's 3500 but it can depend on your weight. Many diets will keep you at 1500 calories per day because you will burn more than that from normal activity ... like 2000+/day. if you exercise you will burn more than that.