For reference, I'm 5'10 and 170 lbs with a very athletic build. My chest is around 42, my waist is 29 (I have a very large chest-to-waist ratio). I normally buy all my shirts in Adult Medium size. Lengthwise, Medium usually fits either right on or slightly too large. Fit-wise, if a shirt is too tight on me, it's at the chest or back. Shirts are almost always too big on the waist for me. Moving onward. My intent with this shirt is for it purely to be a gym shirt. I've used the Amazon Essentials muscle shirts for a year now, and while they're good, they're too tight now. I liked the tightness for its flattery at first, but as I've gotten more muscular, the tightness at the armholes can get discomforting when my muscles are swelling at the gym. The neck size on the muscle shirt was also too small (which, pathetically enough, I hate because it messes up my hair trying to pull it up or down my big head in the changeroom). The overall tightness also provides less airflow and begets more sweat, so I've elected to buy this tank top hopefully alleviate all these issues. After some reading here about the shirts being large, and having owned Amazon Essentials polos and muscle shirts in Adult Small, I decided to go with an Adult Small. It seems to fit well. The chest a bit tight, but unlike the muscle shirts, it's looser, it hangs lower, and the material is softer and stretchier, so it's not discomforting. The shirt shows of a decent amount of your chest from the neck whole, and just a little bit from the arm wholes. Overall, aside from the slight tightness from the armhole on my chest, it's a pretty neutral fit, which is exactly what I wanted. It should be airy enough for what I want. Lengthwise, the shirt is a bit long. I probably could have gotten away with an Extra Small for the length, but I'm worried it would have put the shirt on too much of the tight side. The tank is pretty much going almost all the way down my bum. I guess having a bit of extra length in the gym isn't a bad thing so that your lower back and your stomach aren't sticking out when your shirt rides up during certain exercises, but yeah. The length would be my one issue. The material is very soft and stretchy. It should hinder me nothing whatsoever while at the gym. Overall, I'm pleased with this shirt, especially at this cost. I plan to pick it up in every color available.