DT228 Junior Cut sizing. This retro look is always a comfortable choice.4.8-ounce, 50/50 ring spun combed cotton/poly, 26 singles.  Coverstitch detail at shoulders and hem.
 
(Jr cuts are about 2 sizes smaller then ladies...if you wear a ladies MED, you'd wear an XLG Junior)
 
If you were to lay the shirt down flat, here is sizing... 
Large = 18.5" armpit to armpit
XLarge 20" armpit to armpit
2XLarge 21.5" armpit to armpit
3XLarge 23" armpit to armpit
4XLarge 24.5" armpit to armpit
We've got samples at our shop, stop by and try one on!