PRE-SALE (STARTS SHIPPING WITHIN 2 WEEKS) Life only has one real rule. Don’t be WEAK. We don’t believe building muscle automatically makes you a virtuous person. We’re not here to tell you how to live your life. But the one unforgivable sin is to remain weak. There is nothing lamer than not pushing yourself physically to see what you are capable of. Nothing sadder than untapped potential. That’s the golden rule, don’t be WEAK.   Keep in mind the MAJOR difference in sizing is just the length (most tank sizes in the chest area fit pretty similar). At 5'10 and 180lb, I wear a size Large.I would say the following sizes would work as a rule.If you are below 5'4 (or female) get SmallIf you are between 5'5'-5'10 (and/or a small or medium build) get MediumIf you are between 5'7-5'11 (and/or a medium+ build) get LargeIf you are between 5'9-6'1 (and/or have quite a lot of muscle) get X-LargeIf you are 6'0+ (until maximum height 6'5) get XXLWomen should wear the S or M. Most guys are either M or L (or if you are jacked/are taller, XL). Personally I like to wear the L or XL (whereas for t-shirts I usually wear a M or for leg day a L).Made of 88% Polyester, 8% Raylon, 4% Spandex. Machine wash on cold.