Long Plus-Size Formal Prom Dress with Beaded Collar Measurements for size 20 women are as follows,armpit 27,length from the back of the neck 58,back to back 19,sleeve from shoulder (arm hole)10,length from shoulder 58,around the arm muscle 0,waistline44.size 18w, Measurements are as follows,size medium,armpit 25,,length from the of back neck 60,and front neck 56,back to back 19,sleeve from shoulder (arm hole)8,waistline 42, hip 50.