Size Spec	Small	Medium	Large	X Large
Length	31	41	51	61
Chest Width	24	29	34	39
Hem Width	27	32	37	42
Back Neck Width	16.5	18.5	20.5	22.5

Examples of dog sizing:-

Dog	               
Chuhuahua          Small
Jack Russell       Medium
Cocker Spaniel     Large
Border Collie      X Large