Cigarettes vary in rod length but are generally thought of as a constant unit. In this study, we evaluated whether the rod length of participants' usual brand cigarettes affected their perceptions and smoking habits when switching to SPECTRUMs. Data were analyzed for 341 participants smoking their own brand cigarettes for one week and after switching to normal nicotine content (11.6 mg) SPECTRUMs for 2 weeks. Changes in perceptions of cigarette attributes and biomarkers of smoke exposure were evaluated using linear mixed models among 3 groups: usual length short (ULS, 72 mm); medium/king (ULM, ~84 mm); and long (ULL ≥ 100 mm). Among the 3 cigarette length groups, only ULL smokers' rated SPECTRUMs significantly less strong, harder to draw, lower in taste, and lower in enjoyment (p < .03) compared to usual brand. Among all groups, satisfaction was significantly lower for SPECTRUMs (p < .02). Cigarettes per day (CPD) increased significantly more for ULL (+4.75 CPD) as compared to ULM (+1.38 CPD) (p < .001). When switching to SPECTRUMs, cotinine-per-cigarette decreased among all groups, and exhaled carbon monoxide increased significantly in ULL and ULM smokers (p < .001). People who smoked long cigarettes had the largest changes in perceptions and use when switching to SPECTRUM research cigarettes.