Life time smoking of ready made cigarettes can be readily quantified as "pack years" smoked, but methods for measuring loose tobacco use are less well established. In this study the frequency of loose tobacco use by 247 hospital in-patients was determined; 64% were current or ex-smokers, 41.3% of whom (25.9% of participants) had smoked loose tobacco. A formula was developed for converting loose tobacco use to pack years smoked, based on the weight of tobacco in ready made cigarettes; 12.5 g or half an ounce of loose tobacco was approximately equivalent to one packet of 20 cigarettes. Using a questionnaire it was found that hospital physicians of all grades were able to convert smoking histories of ready made cigarettes, but not loose tobacco, into number of "pack years" smoked.