Researchers in the US have calculated how much pot there is in the average joint, and in case you too were wondering, the answer turns out to be 0.32 grams of marijuana in your typical funny cigarette.

But, wait a sec… why do scientists need to know this exactly? (And no, it's not because they're on their way to a party and need to figure out exactly how much weed they need to bring.)

"It seems like an odd question but major policy questions depend on the answer," explains criminologist Greg Ridgeway from the University of Pennsylvania.

After all, there's a tonne of scientific research always being conducted on marijuana and its potential effects on health, and since many weed users gauge their consumption purely in terms of how many joints they've smoked, it'd be helpful if scientists, health workers, and law enforcement officials actually had a rough idea of how much pot that actually amounts to.

Up until now, there hasn't been a lot of consensus. According to Ridgeway, prior estimates have put it anywhere between 0.3 grams and 0.75 grams of cannabis. Previous research has estimated 0.66 grams, and the US Office of National Drug Control Policy has suggested both 0.43 and 0.5 grams.

And none of this necessarily corresponds with what weed smokers themselves think. A poll run last year by High Times found respondents thought their joints contained anywhere from 0.1 grams to 1 gram of weed (with most leaning toward the latter amount).

"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," Ridgeway explained to Niraj Chokshi at The New York Times.

Ridgeway and fellow researcher Beau Kilmer from the non-profit RAND Corporation arrived at their own figure by going through a database of more than 10,000 marijuana transactions recorded from Justice Department interviews with people arrested on drug-related charges, covering a period of 11 years from 40 communities in the US.

"The data had information on 10,628 transactions related to marijuana," Ridgeway said in a press release. "Some will tell you about loose purchases, in grams or ounces, and give you a dollar amount. Other people will say, 'I bought four joints and paid $20'."

With the interview data in hand, the researchers used a pricing model to account for factors like inflation, pricing differences in different markets, and even factors like bulk discounts from drug dealers. "When people buy an ounce [28.3 grams] of marijuana, they get a real volume discount," Ridgeway told The New York Times.

Once they put the data through the model – called the Brown–Silverman drug pricing model, which originated in the '70s – the team was able to "untangle weight and price, to estimate the average joint weight," Ridgeway says. "That all boils down to about 0.3 grams, which is much less than previously thought."

While the figure may be less than some previous estimates, it could turn out to be crucial in helping inform all kinds of research and policy programs, whether tracking illicit sales of marijuana in places where the drug is illegal, or helping to quantify pot volume in places where it isn't.

"It turns out to be a critical number in estimating how much marijuana is being consumed [nationwide], how much drug-trafficking organisations are putting on the market, and how much states might expect in revenue post-legalisation," says Ridgeway.

Of course, there's a lot more involved in pot consumption than just weight, as the strength of the drug can also vary greatly.

"Tetrahydrocannabinol, or THC, the chemical that produces the main psychoactive effects of marijuana, matters," Chokshi writes in The New York Times. "And, like weight, THC content fluctuates."

But that's a challenge for other research to solve – and with the effects of cannabis being studied in everything from IQ tests to Alzheimer's research and teen smoking habits, every little bit of extra understanding helps.