We can take a pretty educated guess at how some celebrities will spending this weekend.

Tomorrow is 4/20, otherwise known as the international day to smoke up. And in the land of Hollywood, where medical marijuana cards are as commonplace as drivers licenses, it's safe to say that plenty of celebrities will be, umm, "celebrating." Not only that, but these A-listers are pretty open about their love of Mary Jane, going on the record in interviews as avid pot fiends.

Check out our roundup of the 20 "greenest" celebs who will definitely be celebrating 4/20!

Related Article: Justin Bieber "Trying To Be Better" After Pot Photos Surface

1. Snoop Lion (Dogg)

Related Article: Chris Brown Toking And Driving After Grammys

Snoop is the undisputed king of the sticky-icky-icky. He's photographed more often than not with a blunt in hand and even released his own line of rolling papers. However, changing his name from Snoop Dogg to Snoop Lion proves that it is in fact possible to smoke too much weed.

2. Lil Wayne

Weezy freely admits that he's been a chronic pothead for the last 20 years and shows no signs of slowing down. He's also taken a page out of Snoop's playbook and used countless photo shoots as a chance to put a blunt in his mouth. Hey, it's safer than Sizzurp, right?

3. Chris Brown

How much of a pot fiend is Breezy? Not only is he unable to wait to smoke until he gets home, choosing instead to toke behind the wheel, but he obviously needs three blunts at once to satisfy his cravings.

4. Rihanna

Being an island girl, we shouldn't be totally surprised that RiRi smokes pot. When initial photos surfaced of her with a joint between her fingers, she tweeted that she was going to respond to the scandal but "ran out of f*cks to give."

5. Kristen Stewart

In the July 2012 issue of Vanity Fair, Kristen labeled herself as a "weirdo" with an avid love for pot. “You can Google my name and one of the first things that comes up is images of me sitting on my front porch smoking a pipe with my ex-boyfriend and my dog,” she says. “It was taken the day the movie came out. I was no one. I was a kid. I had just turned 18.”

6. Seth Rogen

Seth admitted to David Letterman that he started smoking at 13 and is pretty much high at all times throughout the day now. He's also a major advocate for the full legalization of marijuana.

7. Kirsten Dunst

In a 2007 interview, Kirsten admitted to enjoying her reefer and declared that "the world be a better place if everyone smoked."

8. Morgan Freeman

Morgan admitted that he has ceased using hard drugs, but that he will "never give up the ganja." He's also worked for years as a medical marijuana advocate.

9. Lady Gaga

During a show last September in Amsterdam, Gaga raved to fans about the benefits of marijuana and said she indulged in a couple of the city's famed coffee shops. "I want you to know it has totally changed my life and I've really cut down on drinking," she said. "It has been a totally spiritual experience for me with my music."

10. Charlize Theron

We've seen plenty of innovative ways to smoke pot, but Charlize took the cake when she was pictured smoking out of a green apple.

11. Miley Cyrus

Miley was responsible for a huge increase in salvia sales when she was videotaped using the drug in 2010, but has since moved on to weed. Not only has she been photographed smoking blunts on several occasions, but she even teamed up with the king of pot himself, Snoop Lion, for a reggae track titled "Ashtrays & Heartbreaks."

12. Lindsay Lohan

Lindsay has never talked about her pot use, but we weren't the least bit surprised to see this photo of her last year releasing a billowing cloud of pot smoke. She may have to take a breather when she heads to rehab next month though...

13. Amanda Bynes

Amanda may have a more serious problem with pot than we initially realized. Not only was she photographed allegedly smoking up behind the wheel last summer, but she was reportedly kicked out of her NYC apartment earlier this year for letting her pad reek of weed at all hours of the day. Marijuana use would definitely explain some of her behavior and choice of photos to post to Twitter...

14. Matthew McConaughey

Matthew was busted at his Texas home in 1999 for getting high and playing the bongos naked. There are certainly worse crimes, but it's no surprise that those two activities go hand in hand.

15. Michael Phelps

After cleaning up at the 2008 Beijing Olympics, Michael was putting those swimmers lungs to a different use the following year. He apologized shortly after this photo was released in 2009 and pulled it together in time to win gold at the 2012 London Olympics. Now that he's officially retired from the sport, though, all bets are off.

16. Wiz Khalifa

Parenthood has not convinced Wiz to give up the green. He and wife Amber Rose have decided that he will continue his toking ways and that their child "will know that Daddy likes to smoke."

17. Joan Rivers

During a 2012 episode of her reality show Joan and Melissa: Joan Knows Best?, the comedy icon was filmed smoking from a pipe to relax. She later described the experience as "fabulous," but said she couldn't do it often because weed "puts on pounds."

18. Alanis Morissette

Alanis dated a medical marijuana advocate in 2009 and was featured in High Times Magazine, where she claimed that pot helps her with songwriting. "As an artist, there's a sweet jump-starting quality to [marijuana] for me," she said. "I've often felt telepathic and receptive to inexplicable messages my whole life. I can stave those off when I'm not high. When I'm high — well, they come in and there's less of a veil, so to speak. So if ever I need some clarity... or a quantum leap in terms of writing something, it's a quick way for me to get to it."

19. Justin Bieber

Photos of Justin smoking pot surfaced this past January, which he later indirectly apologized for. “i see all of u. i hear all of u. i never want to let any of you down. i love u. and..thank u. #beliebers,” he tweeted. Considering some of his more recent behavior, we'd love it if smoking pot were the worst of his issues.

20. Willie Nelson

The grandfather of celebrity pot smokers, Willie has been arrested numerous times for possession of the drug and has served as an advocate for legalization for decades. He's also known for smoking his own strand of marijuana called "Willie Weed," which many have attested to being among the strongest they've ever smoked.

Which celebrity do you think is the "greenest?"

Photos courtesy of Getty Images, TMZ, Twitter, WE TV and High Times Magazine