Think in proportions.
Look at the shoulder, the body and the hem together. A shoulder seam that sits further down the arm creates a different outline from one that follows the edge of the shoulder. A wider body adds room; a shorter hem changes how that room sits above a trouser.
Oversized is a silhouette, not simply an instruction to buy a larger size. Decide how much room you want through the body and where you want the hem to finish.
Use a piece you know.
Lay a hoodie you like flat, without stretching it. Measure across the chest from underarm to underarm, then from the high point of the shoulder to the hem. Compare those garment measurements with the guide for the style you are considering.
Keep body measurements and garment measurements separate. A flat chest width is half the distance around the garment; it is not the same as a chest measurement taken around your body. The published AVERLEN size table is illustrative during this preview and should not be used to choose a real purchase.
Make space for the day.
Think about the layer underneath. A tee asks for less room than a heavier long sleeve. Check the sleeve length with your arms relaxed, then with your arms reaching forward. A fit should make sense in motion as well as in a mirror.
Finally, look at the whole outline. A generous top with a straight leg feels different from volume through both pieces. Neither is a rule. The useful question is whether you feel comfortable wearing it your way.