Here are the measurements for our adult unisex sizes:

Small (18" armpit to armpit x 25" overall length)
Medium (20" armpit to armpit x 27" overall length)
Large (22" armpit to armpit x 29" overall length)
XL (24" armpit to armpit x 30" overall length)
2X (26" armpit to armpit x 31" overall length)
3X (28" armpit to armpit x 32" overall length)
4X (30" armpit to armpit x 33" overall length)
5X (32" armpit to armpit x 33" overall length)