As this style brief is Asian Size,smaller than US size.You can view the size table below before making decision.
Size Waist Range
M 25.9" - 29.1"
L 26.7" - 29.9"
XL 27.5" - 30.7"
You know the brief is elastic,so if your waist is 27",you can choose Size M if you want to wear it more slim,you can choose Size L if you want to wear it more loose. 
