I had to measure this differently as its not only open but crosses the body and as such is so very flexible size wise. Its probably one size fits most but here are some numbers to give you and idea…
Shoulder to shoulder: About 31″
I measured straight across the back from armhole to armhole, this is NOT doubled, just straight across: 23.5″
Waist: free
Hip: free
Shoulder to bottom hem: 31″