You mean, "what is the fat content of butter when only the fat is left?" Is this a trick question?

Regular churned butter has at least 80% fat; we've see it as high as 86%. The remainder is water, milk solids, and salt (if that has been added). If you clarify the butter and get rid of most or all of the water and other bits, you actually increase the relative proportion of fat and boost the calorie content significantly. Salted butter has 100 calories per tablespoon, unsalted butter has 102, and clarified butter has 126.

Now you're sorry you asked, aren't you?