You can convert the percentages of fats, carbohydrates and proteins of your diet into the number of grams of each of these calorie sources. This will also require you to know the number of calories you can consume each day. You’ll typically perform this calculation when you’re following a diet that specifies the percentages of fats, carbohydrates and proteins to eat as well as your daily caloric intake.
Obtain the percentages of fat, carbohydrates and proteins that your diet allows. The composition for a typical diet is 30 percent fat, 50 percent carbohydrates and 20 percent protein.
Determine your daily caloric intake from your diet. A typical diet will allow you to consume 2,000 calories each day.
Calculate the number of calories that you should get from fat, carbohydrates and fats each day. Your diet allows 2,000 calories per day and 30 percent of your calories should come from fat. You may therefore get 0.30 x 2,000 = 600 calories per day from fat. Similarly, you’ll get 0.50 x 2,000 = 1,000 calories from carbohydrates each day. Your protein requirement is 0.20 x 2,000 = 400 calories per day.
Derive the number of grams of fat, carbohydrates and protein you’re allowed each day. Each gram of fat has 9 calories and your daily fat allowance is 600 calories. You may therefore have 600 / 9 = 67 grams of fat each day. Each gram of carbohydrates has 4 calories and your daily carbohydrate allowance is 1,000 calories. You may therefore have 1,000 / 4 = 250 grams of carbohydrates each day. Each gram of protein has 4 calories and your daily protein allowance is 400 calories. You may therefore have 400 / 4 = 100 grams of protein each day.