The correct size for the ball in WNBA ( Women 's National Basketball Association ) rules is a minimum of 28.5 inches ( 72.4 cm ) in circumference . This is 1.00 inch ( 2.54 cm ) smaller than the NBA ball . The regulation WNBA ball is a minimum 28.5 inches ( 72.4 cm ) in circumference , which is 1.00 inch ( 2.54 cm ) smaller than the NBA ball .