Nami has a tattoo on her left shoulder which represents mikan and pinwheels (a homage to her past), where she used to have a tattoo for being a member of Arlong's Crew. Near the beginning of the series, Nami wore thick, low cut leather boots and a simple blouse. However, during the Arlong Park arc and thereafter, Nami wore open-toed shoes and more revealing outfits (With the tattoo no longer being a secret). As of Chapter 435, Nami changed her shoes to high heeled boots. She usually pairs her tops with skirts with rings on them. Her overall physique 'matured' suddenly (according to Oda, this is so because she is only 18 and still in her "growth phase").
According to the author (in response to a fan's question), Nami's dress size was 34-22-34. The author has also replied to a fan's question to saying that right now Nami's measurements are as follows: Height 169 (5'6.5) B 95 W 55 H 85, though her breasts seem to grow and then "reset" throughout the arcs (this is much more obvious in the manga).