The barrel is the thickest part of a bat, where contact with the baseball generally happens. Barrel size is determined by diameter, varying from 2 1/4“ to 2 5/8“. The upside of a larger barrel is that it provides more surface area to hit the ball, and therefore a bigger “sweet spot.” However, smaller barrels allow for faster swing speeds and better control.
Most baseball leagues provide guidelines for maximum barrel size, but there is always room for personal preference. Generally, younger players between the ages of 5-13 will benefit from smaller barrel sizes (2 1/4" - 2 1/2"), while teens and adults will be more capable of handling bigger barrels (2 3/8" - 2 5/8").