A regulation professional baseball bat can be up to 42 inches long (about 107 cm), but most adult bats in actual use are in the 32–34 inch range.

Official rules

  • Major League Baseball rules state that a bat must be a smooth, round stick no longer than 42 inches in length.
  • The maximum diameter at the thickest part is set a little over 2.6 inches, which keeps bats relatively slim and balanced.

Typical real‑world lengths

  • Most adult and pro players swing bats in the 32–34 inch range, well under the 42‑inch legal maximum.
  • Youth bats are shorter, commonly from about 24 to 30 inches depending on age, height, and strength.

League-to-league limits

  • Little League rules usually cap bats at 33–34 inches depending on division, with specific diameter and weight requirements.
  • High school and college players typically use BBCOR-certified bats around 31–34 inches long.

TL;DR: The longest allowed baseball bat is 42 inches, but the most commonly used bats are about 32–34 inches for adults and shorter for kids.

Information gathered from public forums or data available on the internet and portrayed here.