The average size of the human mouth is 50 millimeters. The size of the mouth varies according to the size of the head. People with larger heads tend to have bigger mouths. As children grow older, the jaw bones tend to widen and the mouth gradually becomes bigger.
The mouth may range from 30 to 70 millimeters. Shorter people tend to have a smaller jaw opening. On average, women tend to have smaller mouths than men, as they are shorter. The size of the mouth is related to the movement of the upper and lower jaw bones. The world’s largest mouth belongs to Francisco Domingo Joaquim who has a 17 centimeter jaw opening.