All measurments are provided on each garment. 
Our double sizes is per below:
XS/S 36-38
S/M  38-40
M/L  42-44
L/XL 44-46

The only items not following this chart is the Poncho outerwear. 
The poncho comes in two sizes S/M and M/L. One smaller, one larger. this because the poncho design does not have any traditional arms, only a 25 cm short seam horisontal on the half round body, under a insewn tube functioning as arm with wide elastic on its edge. The construction of the poncho is very airy and a size S/M can take all from a size 36 and up to a 42 depending on the bust size and length of the body. The differance between the two sizes is 5-6 cm in length all over.