Use the method that is easiest for you. 1  Counting grams of carbohydrate. For example, if you want to eat 45 grams of carbohydrate, you would choose three servings (3 servings x 15 grams per serving = 45 grams). 2  Counting servings of carbohydrate. In this system, 15 grams equals 1 carbohydrate serving.