Something doesn't feel quite right. Let's see what they write in the history books a few years from now. SDK forever.

Measurements are width / height.

Small: 18" / 22"
Medium: 20" / 24"
Large: 22" / 25"
X-Large: 24" / 27"
2X-Large: 26" / 28" 
3X-Large: 28" / 29"