A single red or green grape, which weighs approximately 0.2 ounces, has about 3 calories. A cup of grapes, which is about 5.3 ounces, has 104 calories.
Other nutritional facts to consider about 1 cup of grapes is that there are only 2 calories from fat, no cholesterol and 0.2 grams of fat. Grapes also have a minimal amount of protein at 0.1 grams and 3 grams of sodium. Grapes are a good source of carbohydrates; 1 cup of grapes has 27.3 grams of carbohydrates, which is 9 percent of the recommended daily allowance. That same amount of grapes also has 15.1 milligrams of calcium and 288.4 milligrams of potassium.