It doesn't "take one calorie to burn", you gain one calorie by burning.
Now noting obviously what everybody else has said about selection of the type of fat affecting the precise amount of energy available from one gram (which in practice will be measured in a calorimeter), but what this is really saying is that by metabolising some specified fraction of a gram of fuel you can do (approximately) one calorie of work, e.g. raising the temperature of water by some specified amount or moving your muscles in such a way that they lift a weight by some specified number of centimeters.
So no, it's not an integer: it's an approximation to the amount of work you'd have to do to prevent the food you've just eaten being stored as flab, and to get an accurate figure you'd have to do an assay of an identical portion of that food taking into account both its chemical composition and its digestibility (e.g. an increased amount of fibre in the specimen might not change the result of the physical calorimetric test, but might change the availability of the nutrients to the digestive system).