The size chart.

Measurements are in centimetres, for a shirt laid flat and then doubled at the chest. Match a kit you already own.

Size	Chest	Length	Shoulder
S	96	69	42
M	102	72	44
L	108	74	46
XL	114	76	48
XXL	120	78	50

Chest is the full way around, measured under the arms.
Length runs from the top of the shoulder seam to the hem.
Shoulder is seam to seam across the back.