I’m generally a size M in Korean pants (including 66girls) due to my bigger thighs, but I decided to size down to a S for these after reading the reviews on the Korean website. Glad I did because they fit me perfectly. The waist is elastic so it fits tightly, but the pants are wider around the leg. Average thickness so I think it will be good for fall/winter. For reference I wear 26-27 in US sizes.