I've always found it most useful when clothing makers note the specific measurements of a garment. Every garment is different. Even many vendors typically show only the generic shirt/pants sizing charts, sometimes narrowed by maker, almost never narrowed to that specific garment. I, too, have found many of the generically sized items to be woefully deficient as compared to other garments in that same labeled size.
About the best measurements I've found:
- The length from shoulder seam to shoulder seam (left to right, over the back of the neck/collar area.
- The width of the garment from armpit to armpit. Roughly double to get a reasonable estimate on a generous fit, though somewhat smaller might well fit you a bit better (depends on the person).
- The width of the garment just above the belt line;
- And, height, from the back of the neck/collar area to the tail.
If these are on, as measured on the actual garment, I almost always find it fits decently well. Irrespective of what the label says.