Selecting a baseball bat is often a very subjective process. You just have to try out a variety of sizes and weights to determine what feels best. However there are some basic concepts to consider. If you are big and strong you can wield a heavier bat. A smaller player can benefit from an increase in their bat speed with a lighter bat. A longer bat provides greater reach for outside pitches, but it is also heavier, which can slow down your swing. Striking the right balance between power and speed is a matter of trial and error.
Youths 12 years old and younger usually use a bat with a 2 1/4” diameter barrel. This is the standard size for Dixie Youth and Little League baseball. High schools and colleges restrict the barrel diameter to a maximum size of 2 5/8”. All leagues have their own bat requirements, so always check to learn the rules before you buy a bat.
As mentioned earlier, you have to test out a bat to determine if it is going to work well for you, but here are some basic guides for bat length based on age. Most 5-7 year olds use a 24”-26” bat. 8-9 year olds usually use a 26”-28” bat. 10 year olds typically swing a 28”-29” bat. An 11-12 year old generally uses a 30”-31” bat. 13-14 year olds usually wield a 31”-32” bat and 15-16 year olds often use a 32”-33” bat.