Start with length
BBCOR is a −3 standard, which means weight is locked to length: a 32-inch bat weighs 29 ounces, a 33 weighs 30, and so on. You are not choosing a weight. You are choosing a length, and the weight comes with it. These are reasonable starting points.
Height is a proxy for arm length, not for strength. A thick, strong 5′10″ hitter may be better off at 33 inches; a lean 6′1″ sophomore may be much better off at 32.
The twenty-second test
Hold the bat straight out at arm’s length. If the barrel drops, go shorter.
Grip the knob, extend your lead arm out to the side, parallel to the ground, and hold the bat horizontal for twenty seconds. If the barrel sags before you get there, that bat is too much for you right now. It is a crude test and it works — it measures exactly the thing that fails in the batter’s box, which is the ability to hold the barrel in the zone through a full swing.
The second test is simpler: take twenty swings. If the last five look worse than the first five, the bat is too heavy or too long.
Three things worth knowing
The extra ounce buys almost nothing
At BBCOR the barrel is capped, so a longer, heavier bat does not give you meaningfully more exit velocity the way it might in a travel-ball bat. What it does give you is a slower swing and a later decision. A player who can control a 32 will out-hit the same player fighting a 33 more or less every time.
Half sizes exist, but only in one place
The Atlas 2.0 offers 32.5 and 33.5 inch options. Nothing else in this guide does. If a hitter is genuinely between sizes, that is a real reason to look at that bat first.
Buy for the player you are now
A growing sophomore is almost always better served by the size that fits this spring than by the size he might grow into next spring. He will get a full season of good swings out of the right bat and a full season of bad habits out of the wrong one. The bat is cheaper than the habits.