How Big Is a Roulette Ball?

A roulette ball is a small, hard, round object that is spun around a circular track by a croupier in a casino game of roulette. The ball eventually comes to rest in one of the 37 or 38 numbered and colored pockets on the wheel.

The outcome of each spin is determined by the number and color of the pocket into which the ball falls.

The size of a roulette ball is dictated by the size of the wheel with which it is used. A standard roulette wheel has a diameter of about two feet, and therefore a roulette ball must be small enough to fit comfortably inside this circumference.

Most balls are between 18 and 21 millimeters in diameter, which is just over three-quarters of an inch. This size allows the ball to roll smoothly around the track without bouncing too high or falling off the edge.

A roulette ball must also be heavy enough to make spinning it around the track a relatively easy task for the croupier. If the ball were too light, it would be more likely to be affected by air resistance and other forces, making it more difficult to predict where it would land.

A heavier ball is less affected by these outside forces and therefore spins more predictably. Most balls weigh between 17 and 18 grams.

The material from which a roulette ball is made also affects its spinning characteristics. Early balls were made from ivory, but this was quickly replaced by Bakelite, a type of plastic that was both strong and resistant to temperature changes (which can cause warping).

Today, most casino-quality roulette balls are made from acetal, nylon or phenolic resin, materials that combine strength with smoothness and resistance to warping due to temperature changes.