Let's get straight to it — here's what actually matters on this one.

• A shoulder seam should sit exactly at the edge of your shoulder bone — if it droops onto your upper arm, the shirt is too wide across the shoulders.
• This is one of the hardest fit issues to alter after purchase, since it involves the garment's core structure, not just hemming.
• A dropped shoulder seam restricts natural arm movement and creates extra bunched fabric at the underarm, a high-friction, high-sweat zone.
• If this happens consistently across brands, look specifically for 'slim' or 'tailored' fit lines rather than 'classic' or 'relaxed' cuts.

The fit-and-fabric-health takeaway: Correct shoulder fit is foundational — every other measurement, and how the fabric breathes at the underarm, depends on getting this one right.

Next up: check out our guide on why your t-shirt shrinks after one wash.