Size chart shows your actual body measurements not that of the jacket itself.  The fit is for the maximum measurements below. Size up if you prefer a more roomy fit, are between sizes or wish to wear thick clothing underneath.

8-10 best for bust 33-35”, waist 26-28”

12 best for bust to 37”, waist to 30”

14 best for bust to 39”, waist to 32”

16 best for bust to 41”, waist to 34”

18 best for bust to 43”, waist to 36” 

20 best for bust to 45”, waist to 38”