Where the shoulder seam should sit

Short answer: On the edge of the shoulder, where the arm begins. Set inside that and the garment pulls. Set outside it and the shoulder looks wider.

The simplest fit test

Put a finger on the bony point where shoulder meets arm. That is where the seam should sit. This single check tells you more about fit than chest width does, because everything else hangs from the shoulder.

When the seam sits too far in

The garment pulls backwards, tightens across the shoulder blades and binds when you reach forward. A larger size does not fix it if the cut is too narrow, only a different cut does. See bamboo t-shirts for men.

When the seam sits too far out

The sleeve hangs on the upper arm and the shoulder line disappears. That is intentional on oversize and drop shoulder styles but a fault on an ordinary cut. See bamboo t-shirts for women.

Raglan is an exception

Raglan sleeves have no shoulder seam. Here the seam runs diagonally from neck to armpit, and you judge fit by how the sleeve falls instead. See sweat clothing.

Frequently asked questions

Can a shoulder seam be moved

Yes, but it is an expensive alteration. Choosing a different cut is easier.

Does the rule apply to shirts too

Yes, and even more strictly, because shirt fabric does not stretch.

What about oversize styles

There the seam sits on the arm on purpose. Judge the sleeve length instead.