An average medium-sized gala apple weighs 140 grams and contains 80 calories. It also has 22 grams of carbohydrates with 5 grams of fiber and 17 grams of sugar. One medium-sized Gala apple provides 195 milligrams of potassium. It also provides as 2 percent of the daily value for vitamin A, calcium and iron, as well as 20 percent of the DV for vitamin C, based on a 2,000-calorie diet.