American clothing

Is it just me or are American clothing smaller? My sister just got back from Arizona and brought me back a pair of cute sweatpants. Now I usually wear a small to medium and my sister is bigger than me. The pants she got me are a size large and they just fit. A little tight in the waist and just long enough in the length. Also I'm not very tall either. I'm only 5'2". I should add that I'm Canadian. Lol. But was just curious.