This yahoo blog has a link to a great site that has a free bat size chart.

This chart will help you determine what size youth baseball bat your son needs to hit the ball harder. Don’t waste money on baseball bats till you have seen the chart and read the tips.
http://youth-baseball-bats.youth-baseball-equipment.com/youth-baseball-bat-size-chart/

You can spend a lot of hard earned money on youth baseball bats, so it is best to get expert advice.
Free Youth Baseball Bat Size Chart and Tips on How to Choose a youth baseball bat