Monkey, it depends on a lot of things, how much you eat, how quick you metabolise foods, what other activities other than running you do and probably a whole host of other things.
I don't think you can really give exact figures. But to give you my own experience, I train for at least an hour every day, 2-2.5 hours on a sunday (if I don't have a race), and one day off in a week. My sessions vary in effort and intensitiy.
Through running (this is the only activity I do now) I have lost three stones since I took up running last year. I was 20% body fat when I started and I am now at 10.5%.
If you are just starting out, then you have to start small, overdoing it will only lead to injury and illness. Start gradually and build up mileage; the golden rule being never add more than 10% of the previous weeks mileage to the current week.
You may find you are getting more hungry as you build mileage, this is fine, as I also eat more now than I did when I was three stones heavier. Although now, like yourself, I eat well.
Good luck with it, let us know how you get on.
Its a basic equation you have to use more than you eat but try not to get obsessive about this. If you don't eat enough them your BMR starts to slow down and your body can go into starvation mode then it becomes counter productive.
Generally the best way to lose fat/weight is to reduce your calorie intake slightly and increase your activity levels gradually.