Well depends on where you look, but this explanation seems to be the most commonly accepted one:
* "Police dispatch code for smoking pot is 420". The number 420 is not police radio code for anything, anywhere. Checks of criminal codes suggest that the origin is neither Californian nor federal. For instance, California Penal Code 420 defines as a misdemeanor the hindrance of use of public lands.
*" There are approximately 420 active chemicals in marijuana". Actually, there are approximately 315 active chemicals in marijuana. This number goes up and down depending on which plant is used.
* "April 20th is National Pot Smokers Day". Well, it is now; but that wasn't the origin.
* "April 20th is Hitler's birthday". Yes, it is his birthday. But, as 420 started out as a time, not a date, his birthday had nothing to do with it.
* "April 20th is the date of the Columbine school shootings". This happened after the term was already in use. May have been why the date was chosen.
* "4:20 is tea time for pot-smokers in Holland". Tea time in Holland is at 5:30 pm, or is it 2:30 pm? Seems no one is quite sure when the wonderful people of Holland drink their tea.
The Origin Revealed
According to Steven Hager, editor of High Times, the term 420 originated at San Rafael High School, in 1971, among a group of about a dozen pot-smoking teens who called themselves the Waldos, who are now pushing 50. The term was shorthand for the time of day the group would meet at the campus statue of Louis Pasteur to smoke pot. Intent on developing their own discreet language, they made 420 code for a time to get high and its use spread among members of an entire generation. A quote from one of the Waldos in the High Times article states, "We did discover we could talk about getting high in front of our parents without them knowing by using the phrase 420."
So it literally started as a grass roots phrase and just caught on.
Either way today has become a national day of honoring the weed and pushing for legalization. Several spots in California have festivals with fields full of people smoking pot together, nothing more in common than a love of the smoke.
So yeah, Happy High Holy Day. Smoke one for me!