In the USA and the UK the government recommend that the average man eat an average of 2500 calories per day (2000 if you are a lady).
What does 2500 calories represent? Its the number of calories that a man of average height and weight would burn by sleeping , watching tv and pottering around the house. In other words, doing no excercise!
Of course, if you are shorter than average you need less. This neat gizmo calculates your resting calory needs. Mine is 2500 but then I'm Mr average.
So, once you know your lazy calory burn, you have a