Anteroposterior Diameters Mnemonic: Larger the alphabets, larger the diameter (V>F>B) Diameters with "sub" prefix are smaller than counterpart without it. mento-Vertical: 14 cm SUB-mento-Vertical: 11.5 cm occipito-Frontal: 11.5 cm SUB-occipito-Frontal: 10.5 cm sub-occipito-Bregmatic: 9.5 cm