What Is the Size of a Baseball?

Regulation baseballs are made according to very strict standards. The balls include cork, wool, cotton-polyester and leather. The composition of a baseball has evolved since the size and weight became standardized in 1872.

Regulation baseballs have a diameter that ranges between 2 7/8 and 3 inches. They have a circumference of between 9 and 9 1/4 inches and they weigh between 5 and 5 1/4 ounces.

Beginning in 1910, the center of a regulation baseball is a piece of cork, called a pill, which replaced the rubber center that was used from 1900 to 1910. The pill has a diameter of 2.06 centimeters and a circumference of 10.47 centimeters.

To keep the ball perfectly round after being hit over and over by a bat when it travels at around 90 miles per hour, the pill at the center of regulation baseballs are wrapped with four layers of yarn. Even the color of the yarn is specified by the industry standards. First, gray woolen yarn is wrapped over the pill. The yarn in this layer is four-ply. The next two layers each use three-ply woolen yarn: first white followed by gray. The final layer is made from white cotton-polyester yarn.

Cowhide from Holstein cows is the preferred leather used to make the outer covering of a regulation baseball. The hide is tanned using a process with alum, and then it must be dyed white. Until 1974, though, horsehide was used to make this covering.

Even the length of the thread used to stitch the leather covering of regulation baseballs is standard. It must be 88 inches long. The thread must also be red and be covered with a protective coating of wax. Not only does the wax help to lubricate the thread as it passes through the leather, it also strengthens and makes the thread water-proof.