It would be nice if t-shirt sizes were standard, and that if every time you picked up a size medium in any store, it was exactly the same size. Unfortunately, a medium in some stores is the size of an extra large in other stores.
Because of the raging disparity in what the size label actually means, it’s difficult to determine what size t-shirt you should be wearing.
A t-shirt that fits correctly should be neither too tight nor too loose. If it’s too loose, it’ll hang on you like a box and look completely unflattering. If it’s too tight, it’ll look like you’re squeezed into it and are about to burst the seams at any point — a look that will almost certainly come across as conceited and annoying.
2. Shoulder Seams
The shoulder seams are a good way to tell how well a shirt fits you. Ideally, these seams should reach to the end of your shoulder at the very top of your arm. If they extend down your upper arm, the shirt is too big. If they don’t reach the end of your shoulder, the shirt is too small.
The sleeves should extend about halfway down your upper arm. If you’re exceptionally tall, you might be safe wearing sleeves that are slightly longer, as these will look more proportional.
The bottom hem of your t-shirt shouldn’t hit any higher than your hips, or it’s too small. It should cover your waistband and extend a few inches past that. If it’s shorter than that, it’ll look like a crop top when you raise your arms. If it’s longer than that, it’ll look like a dress. When trying on a t-shirt, make sure you raise your arms to see how far it rides up.
Many cheap t-shirts have no shape to them at all. They hang like boxes when you put them on and are extremely unattractive. Search instead for a t-shirt that follows the lines of your body a little more. Avoid any that are cut in the shapes of large squares.