According to InnerBody, the actual size of the stomach varies from person to person, but on average it's big enough to contain around 1 to 2 liters of liquid and food during one meal. The stomach can expand to hold around 3 to 4 liters.
Inner Body says that filling the stomach to its maximum capacity is known as overeating. When the stomach has been stretched to its maximum size, digestion takes longer, and this is usually where digestion difficulties come into play. Doctors believe that digestion problems from overeating are caused by the stomach being unable to contract normally to mix the food.