You would be surprised at how few calories one pound of muscle burns in a day. Science used to say 30 - 40 but more recent studies show as little as 6 calories per lb. a day.
If you went on a hardcore calorie counting diet for a few months, you would figure it out pretty damn quick. Of course, you would have to know (as precisely as possible) how much bodyfat you had and how many calories were in the food you were eating. You would also have to keep a meal diary and weigh your food.
It can be done with a fair amount of precision--if you are really motivated.