Markwort Weighted 9-Inch Baseballs-Leather Cover (Individually Boxed) As you train, gradually increase the weight of the ball as you build strength in your throwing arm. Color coded cover indicates the ball weight. Weighted baseballs are 9 circumference with varying weights. Leather cover, white stitching. Weighted core. (Size of regulation baseballs are 9 and 5 oz. )