Cannabis retailers should prepare themselves for a minimum doubling of sales on April 20, the stoner’s Fourth of July, according to new data.

The origins of 4/20 are obscure, but the most common story is about a group of 1970s high-school students who’d meet outside their school at 4:20 p.m. to search for a legendary abandoned marijuana crop (which, needless to say, they never found). Whatever its source, 4/20 has become the busiest cannabis sales day of the year, according to data provider Headset Inc.

The origins of 4/20 are obscure, but the most common story is about a group of 1970s high-school students who’d meet outside their school at 4:20 p.m. to search for a legendary abandoned marijuana crop (which, needless to say, they never found). Peter J Thompson

It was the industry’s single biggest day of sales in 2018, with sales up 111 percent compared with the four Fridays before and after the holiday, according to Headset, which compiled sales data from Washington state, California, Nevada and Colorado.

By comparison, beer sales during the two-week period including July 4 were up 33 percent versus an average two weeks in 2018, according to Nielsen Holdings Plc, which has partnered with Headset to analyze the U.S. legal pot market for consumer packaged-goods companies.

Sales on April 20 don’t appear to be affected by the maturity of the legal market. Each of the four states examined by Headset saw sales at least double last year, when the celebration fell on a Friday, typically the busiest sales day of the week. With April 20 falling on a Saturday this year during the Easter long weekend, retailers should prepare themselves for a rush of customers on both Saturday and “4/20 Eve,” Headset said.

This will also mark Canada’s first April 20 since the country legalized recreational pot last October. Retailers may find it difficult to achieve the same jump in sales as their U.S. counterparts due to the ongoing supply shortages that have plagued the legal market. There will undoubtedly be long lineups, especially in under-retailed cities like Toronto, which currently only has two legal stores to serve its population of nearly 3 million.