The estimates from pot smokers are, shall we say, higher: Roughly one in four people responding to an informal poll last year by High Times, the cannabis magazine, said a typical joint contained one gram of marijuana. But nearly as many said it contained half that amount. Perhaps it depends how you roll.

The actual average may be much less. The new study, an analysis of federal drug arrest data published in the journal Drug and Alcohol Dependence, found the average amount of weed in a joint to be much smaller than those estimates: just 0.32 grams.

Such estimates about more than better understanding a high. Many users report marijuana consumption in terms of joints smoked, a statistic that is useless to researchers, authorities or policy makers without an accurate approximation of what that means.

“In order to get good projections, you need to be able to turn those answers — ‘I’ve had one joint in the last 30 days’ — into a quantity,” said Greg Ridgeway, a professor of criminology and statistics at the University of Pennsylvania who helped write the study with Beau Kilmer, a director of the RAND Drug Policy Research Center.

“These estimates can be incorporated into drug policy discussions,” the two researchers wrote, “to produce better understanding about illicit marijuana markets, the size of potential legalized marijuana markets, and health and behavior outcomes.”