The size of your mask is correlated with the distance from the top of your nose to your chin, not always clothing size.
Measure your face from the top of the bridge of your nose (right between your eyes) around your face and down to just under your chin - to the back of your chin bone (see photo below, I did not have the measuring tape high enough on her nose - she is squirmy!). The sizes correlate roughly to the following measurements. I would recommend the higher size if you are between sizes.
Please message me with questions at email@example.com or message in the Facebook group!
Youth Medium - 4"
Youth Large - 4.5"
Adult Small - 5"
Adult Medium - 5.5"
Adult Large - 6.5"
Adult XL - 7.5"