Most tshirts intended to be worn as an undershirt are very tight and too long for me. I'm not a heavy or short guy. I'm around 5'10 and weaigh around 155lbs.  For me this shirt (size Medium) fits perfectly for tucking in under a button up dress shirt or I could wear it by its self without feeling obligated to wear dad jeans with a pair of velcro tennis shoes from walmart.

I've tried all the hanes and they're all too tight and long. This one fits me well.