The macronutrients -- carbohydrates, protein and fat -- are sources of calories for your body. But carbohydrates should make up the biggest percentage of the calories you get, since they’re broken down into glucose, your body’s main source of energy. By knowing how many total calories you generally consume, you can quickly calculate your carbohydrate needs for the day, so your system gets all the glucose it needs.
Write down everything you eat for a few days. Monitor your portion sizes and keep track of the total calories you consume by following information on the nutrition facts label.
Add up the total calories you consumed in your food log and divide by the number of days. For example, if your total calories come out to be around 6,000 calories in three days, you get an average of 2,000 calories in your daily diet.
Multiply the average number of calories you consume in a day by 45 percent. This is the minimum percentage of your calories that should come from carbohydrates, according to the publication "Dietary Guidelines for Americans, 2010." Write this number down.
Multiply your daily average calories again by 65 percent, which is the maximum percentage of your calories that should originate from carbs. Keep track of this number as well -- now you have a range of calories from carbohydrates you should aim for.
Divide both numbers by 4 because carbohydrates contain 4 calories in each gram. As an example, for a 2,000-calorie diet, you’ll need 900 to 1,300 calories from carbohydrates every day. After dividing by 4, you’ll convert the calories to grams, which is 225 to 325 grams of carbs.
Read the nutrition facts labels on all of the foods you eat. At the top of the label you’ll see the portion size clearly listed. All nutrients on the label are based on a single serving rather than the entire package. Measure out the portion of each food and keep track of the grams of carbohydrates. Continue tracking your carb intake each day to ensure you’re meeting your needs.