The best way to measure your correct size is to compare it to a similar garment you already own.
All measurements in centimeter.

Size	Waist	Length
S	21 - 27 cm	31 cm
M	21 - 28 cm	33 cm
L	21 - 29 cm	35 cm
XL	21 - 32 cm	37 cm
2XL	21 - 34 cm	39 cm