According to About.com, a typical white hamburger bun has 21 grams of carbohydrates. This is seven percent of the recommended daily value. The bun also has 3 grams of protein and 1.5 grams of fat.
About.com also indicates that the amount of carbohydrates in hamburger buns varies somewhat depending upon manufacturer and style. For example, 100 percent whole wheat buns have only 18 grams of carbohydrates, and the protein content is up to 6 grams. "Light," or reduced-calorie, rolls have about 19 grams of carbohydrates. Large hamburger buns, at 30 grams, and flourless buns, at 32 grams, are higher in carbohydrates.