The optimal way to display constituent levels (e.g. tar) on tobacco packaging has not received adequate attention but has important policy implications. Adult smokers and non-smokers (n = 836) were surveyed in France using Computer Assisted Personal Interviewing to assess perceptions of constituent levels displayed numerically (brand-specific tar and nicotine numbers from smoking machines and the current format in European Union), descriptively (a short sentence describing chemicals and their health effects but without any brand-specific numbers) or as a pack insert (a card placed on the inside of the pack describing the presence of chemicals and their health effects in more detail, as well as information on cessation). We also assessed perceptions of identically packaged cigarettes differing only on nicotine levels. Displaying information regarding ingredients either descriptively or on pack inserts was perceived as more comprehensible and informative than displaying them numerically. Numeric yields were associated with false beliefs: almost half the sample perceived packs with lower nicotine levels (0.8 mg vs. 0.9 mg) to be safer.