The length is approximately 7.5 cm ( 2.5 to 3 in ) across the anterior wall ( front ) , and 9 cm ( 3.5 in ) long across the posterior wall ( rear ) , making the posterior fornix deeper than the anterior .
It is about 6 to 7.5 cm ( 2.5 to 3 in ) wide , and 9 cm ( 3.5 in ) long .