 Because I, of course, started looking, okay. What's the longest bat baseball says you can have? I don't know. I'll take a guess and say 38 inches. It's actually 42. Okay. You are not allowed anything over 42. Is anybody actually using that length bat? Funny you should ask that. The longest bats ever measured in history are by Babe Ruth and Joe DiMaggio, who both used 36-inch bats.