Smokers can benefit from switching to less harmful tobacco products, which requires knowledge of relative product risk. However, publicly shared information often emphasizes absolute rather than relative risks. To understand smokers’ perceptions of product risk, we assessed perceptions of various non-combustible products, relative to cigarette smoking, among 31,269 US adult smokers in a series of cross-sectional surveys (2009-2017). Smokers aware of a product rated that product’s risk relative to cigarettes (7-point scale, from "a lot more risky" to "a lot less risky”). Products included snus, other smokeless tobacco, tobacco-heating products, and vapor products (cigalikes, tanks, other vapor products). Logistic regression was used to analyze linear trends among the proportion of smokers who considered each product to be at least as risky as smoking. Analyses also compared risk perceptions of different vapor products. Generally, smokers' perceptions that non-combustible products are at least as risky as cigarettes increased significantly over time. This was true for tobacco-heating products (61% to 66%), cigalikes (39% to 44%), and tanks (43% to 48%); there was no change for other vapor products (45% to 47%) or snus (73% to 73%). Perceived relative risk of other smokeless tobacco declined significantly over time (83% to 80%). Among vapor products, tanks were the most likely and cigalikes the least likely to be rated at least as risky as cigarettes. Majorities, or near majorities, of smokers perceived each of the non-combustible products to be at least as risky as cigarettes. Except for smokeless tobacco, which large majorities deemed at least as risky as smoking, this misperception increased over time. Smokers' misunderstanding of the relative risks of non-combustible tobacco products likely impede harm reduction.