Square

Size (cm)	XS	S	M	L
Width	48	51	54	57
Height	61	63	65	67

To get good measurements, lay the shirt (preferably the one you love) on a flat, hard surface, then if there are any creases, smooth them out as much as possible

Width: place the ruler from the bottom of the sleeve and measure the width stopping under the other sleeve.

Height: measure from the highest point of the shoulder (top of the collar) to the bottom of the shirt.