Freesize but is made of stretchable fabric, thus will fit small to semi-large frames. 
 
Size Guide (in inches):
 
SMALL
Chest: 32
Waist: 26
 
MEDIUM
Chest: 35
Waist: 29
 
LARGE
Chest: 38
Waist: 32
 
EXTRA LARGE
Chest: 41
Waist: 35
 
You may take your usual size.