UnderArmour definitely tends to prefer their clothes, particularly shoes, run on the small, snug side. Order a larger size if you prefer to have a roomier fit. This is also true if you're ordering for someone with a wide chest, as their tighter fit may be constricting.

Is under Armour true to size?

Under Armour, shoes run pretty true to size when considering width. They do have options that run narrower as well as options that run wider. However, overall their shoes are said to run pretty even all-round. In saying this, Nike shoes do run narrower.

Is under Armour supposed to be tight?

It is a "Compression" fit, so it is supposed to fit skin tight. So others reviewers saying it is too small or too tight simply didn't know what they were buying, and should have purchased a "fitted" shirt.