Question: how to calculate percentage of carbs from total calories?
Answer: Nutrient percentages are the percentage of the day's calories coming from each macronutrient. ... 
Carbohydrate calories = Carbs (g) * 4.0.
Protein calories = Protein (g) * 4.0.
Fat calories = Fat (g) * 9.0.
In the example above, the fat calories per gram are higher than protein and carbohydrates.