How are Baseballs Made?

Baseball is a global sport played and watched by hundreds of millions of people. The vast majority are in North and Central America in countries such as the USA, Canada, Dominican Republic, Cuba, Mexico and Puerto Rico, but it is also popular in Japan, South Korea, China and even The Netherlands. In the USA, Major League Baseball players are revered and the largest baseball stadium - Dodger Stadium in Los Angeles - is packed to the rafters with 56,000 fans every game hoping to catch a home run ball. So how are baseballs manufactured? Read on to find out.

Engineering How It’s Made
28 June 2022

The sport of baseball can trace its roots back to the British games of rounders and cricket. The earliest reference to baseball is from 1744. By the 1830s, there were games being played all over America, albeit without a codified set of rules.

In June 1846 at Elysian Fields in Hoboken, New Jersey, The New York Mutuals beat the Knickerbockers 23-1 in four innings using rules formalised by Alexander Joys Cartwright, often referred to as ‘the father of baseball.’

Using a new set of rules and a leather ball probably stuffed with feathers, the game of baseball was born. It would go on to give the world some of the most famous names in all of sports – including Babe Ruth, Ty Cobb, Jackie Robinson and Lou Gehrig.

Since then, while the bats and the balls themselves have barely changed, the way they’re actually made has been transformed. Here you’ll find the answer to the question ‘how do they make baseballs.’

From String to Strikes - How Baseballs are Made

A close up image of baseball, baseball glove, baseball bat (Photo: krisanapong detraphiphat via Getty Images)

The earliest baseballs were made by the players themselves, and there was no standard size or weight. They would be nothing more than leather pouches stuffed with string or feathers and stitched. They quickly became mis-shapen and waterlogged and didn’t last very long.

In 1876, sporting goods pioneer Albert Goodwill Spalding created a standard for how baseballs are made and his familiar two piece, red-stitched ball was used for decades. In the years that followed other companies took up the mantle, with Rawlings Sporting Goods later becoming the official baseball provider to the MLB.

According to the rules of the game, baseballs used in the professional game have a circumference of between 22.9cm and 23.5cm and weigh between 142g and 149g.

Regardless of the manufacturer, the actual process involved in making baseballs is a little more complex than stuffing feathers into a leather case – and it all starts with a pill.

Stage 1 – The Pill

A baseball starts life as a small ball of cork which is covered with two thin layers of rubber to give the ball its bounceability, this is known as the ‘pill’. The pill is a little smaller than a golf ball and weighs about 25g. The pills are then put into a large drum and coated with a latex adhesive.

Stage 2 – The Yarn

This is where the process of how are baseballs are made gets scarcely believable but we assure you, it’s true! Once the pills are covered with the glue, they are tightly wound with wool yarn and then a fine cotton. The first layer is 110.6 metres of four-ply grey yarn string, the second layer is 41.1 metres of three-ply white yarn and the third layer is 48.4 metres of three-ply grey yarn. Next, a final layer of 137.1 metres of finishing yarn is wrapped around the ball to hold the wool in place.

Yes, you did read that correctly. Each baseball is wound with almost 340 metres of yarn which is almost exactly the same length as the USS Gerald R. Ford, the world’s longest aircraft carrier!

This yarn gives the baseball its resilience, so it can reform to its original shape despite taking a battering by some of the world’s hardest hitters. It’s also wound by precise computers to create a perfectly even surface tension, eliminating what are known as ‘soft spots.’

Once the balls have been wound tightly (known as the ‘centre’) they are put back into the drum and covered with another layer of adhesive glue.

Stage 3 – The Leather

How do they make baseballs? We’re about to enter the final innings… Using a hydraulic press, white cowhide panels shaped like the number eight and punched with holes for stitching are cut out and two are hand-pressed onto the surface of each centre. Then, the balls are clamped into a vice and are double-stitched 108 times (216 stitches) with exactly 223.5cm of waxed red thread.

Stage 4 – The Finish

Once the balls have been stitched they are rolled in a machine to flatten any raised stitches. They are inspected by hand and tested for weight, size and appearance. If everyone is happy, they’re stamped with the maker’s logo and the league logo.

But that’s not the End of the Story…

Batting practice baseballs (Photo: Andy Cross via Getty Images)

One of the most fascinating questions about making a baseball is not exactly how baseballs are made, but rather how they are tested. The MLB has very strict quality control measures in place to ensure each ball is fit to be used at the very highest level. They call it the Coefficient of Restitution, or COR. A sample of each batch of baseballs that come out of the factory is subject to the COR test which involves –

  • Firing the ball at a wooden wall from an air cannon at a speed of 25.9 metres per second from a distance of 2.43 metres. To comply with regulations the ball must rebound at 54.6% of the starting velocity with a margin of error of +/- 3.2%;
  • Being hit 200 times by a force equal to 29.51kg and retaining its shape. It must also distort no more than 0.2cm while being squeezed between two anvils.

This exacting process ensures that when baseballs are manufactured for the MLB, only the very highest quality will be accepted and ready for the stars themselves to strike.


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