Don't assume your usual size translates directly to oversized. That's the number one mistake. Oversized runs differently across brands—and even across styles within the same brand. A boxy cut is not the same as a relaxed cut, and both are different from a drop-shoulder style.

Also, don't use your favorite regular tee as a reference. That fit is tuned for a different silhouette. Instead, compare the actual measurements on the size chart to your own.

And don't forget about shrinkage. Cotton tees shrink, even pre-shrunk ones. If you're between sizes and you plan to machine wash and dry hot, size up. If you air dry, your usual size might be fine.