For fresh berries, use one cup as a serving size. But there's no need to worry about limiting your serving sizes if you eat fresh, raw berries. Adding sugar or high-fat products, like a pie crust or whipped topping, will add not only calories, but fat. Choose serving methods that will provide you with the best source of nutrients and limit fat and sugar. One serving of some berries provides 100 percent of the recommended vitamin C for an adult.
Berries are also rich in potassium.
During the later part of the season, berries will be smaller and less fully developed, but still juicy. Size is also determined by the variety of berry. Some people think that the small to medium berries have better flavor than larger berries. Roadside stands and farmer's markets will provide you a source of fresh raspberries between mid-July through the first part of August. Blackberries will be available for a little longer.