How Many Carbohydrates in a Sweet Potato. 1 Medium Size (2″ x 5″): 103 calories, 24 g carbohydrate, 4 g fiber. 1 Cup (about 200 g): 180 calories, 41 g carbohydrate, 7 g fiber. What’s amazing about sweet potatoes is that they have high fiber content. Technically, you can subtract the grams of fiber from the total amount of carbohydrates to get an idea of the net grams of carbohydrates that we use for energy.