Reference size;
S: Back length 28  CM; chest 41 CM
M: Back length 32  CM ; chest 47 CM
L: Back length 36 CM; chest 52 CM
XL: back length40  CM; chest 57 CM
XXL: back length 44 CM; chest 62 CM 
 
S (recommended weight 3-6lbs)
M (recommended weight 6-9lbs)
L (recommended weight 9--16lbs)
XL (recommended weight 16-22lbs)
XXL (recommended weight 22-30lbs)