How does the energy value of a carbohydrate molecule compare to the energy of a fat molecule?

Fats provide more than twice the energy.

Carbohydrates (including sugars) provide about 4 dietary calories (kilocalories) per gram.

Fats provide about 9 dietary calories (kilocalories) per gram.

Proteins provide about 4 dietary calories (kilocalories) per gram.

Common foods are not entirely composed of these molecules, containing considerable water weight and fiber (no calorie value).