Huffington Post has a graphic up showing about 2,980 metric tons of pot confiscated in 2009. Let us assume that the authorities get 10% of the traffic. So multiply that by 9 to get the total consumption. That gives 26,820 metric tons consumed. A metric ton is about 2,200 lbs. So that is roughly 59,000,000 lbs. If we assume consumption by consumers at a pound a year that gives about 60 million regular marijuana users a year. That is probably a minimum since a pound a year is high consumption. If we assume an ounce a month (still high) that would be about 80 million regular users. At an average of a half ounce a month we get 160 million users (a doubtful number). And of course the ratio of confiscations to total traffic could be off. But 10% is the commonly given law enforcement estimate.

In any case the “fact” of about 15 million regular marijuana users in the US (latest numbers – 2010 – show 17.4 million) are probably on the low end.