I want to get a Medium size in Japanese size, which American size would fit the size??

Tech Specs:

Material:

[membrane/laminate] V-Science (2-layer); [face fabric] mod weave; [lining] V-Science 

Fabric Waterproof Rating:

10,000 mm 

Fabric Breathability Rating:

10,000 g/m?? 

Venting:

inseam 

Gaiters:

yes 

Seams:

fully taped 

Waist:

adjustable 

Pockets:

2 hand, 2 back, 2 front 

Recommended Use:

snowboarding, skiing 

Manufacturer Warranty:

30 days