The ball girth, also called the joint girth, is a measurement of the distance around shoe’s toe box at its widest point, typically at the metatarsal heads (the ball of the foot). It is used to ensure the shoe fits the width of the wearer’s foot, and is commonly used in shoe sizing and fitting. The measurement of the ball girth is taken by placing a measuring tape or ruler across the widest point of the shoe last and measuring the distance between the two sides.
The ball girth is the measurement around the shoe last from the lateral ball point to the medial ball point. The Ball girth is a critical dimension, when measuring a last you need to know the ball girth. The ball girth of a last typically grades at a rate of 1/4 inch and 6.35mm per whole size.