It's not an exact science when watch collecting became a bonafide pastime for some of the world's biggest stars but they're steadily creeping up the haute horlogerie vine as serious investors who sink a small fortune into each timepiece they purchase. Of course, their ever growing collection is buoyed by the fact that these household names are top-billing celebrities who've the deep pockets to upkeep a covetable collection that runs the gamut from Patek Philippes and Rolexes to Panerais and Hublots.

Indeed, you could almost liken watch collecting to stamp collecting... you know, for the rich and famous. So who among the Hollywood elites are these aforementioned horophiles? Take a gander at our roundup and you might just be surprised at some of the names that made the list.

WHO: Leonardo DiCaprio
NOTABLE TIMEPIECES: Tag Heuer Carrera Calibre 1887, Breitling Chrono Avenger, Rolex GMT Master

Celebrity watch collectors Leonardo DiCaprio

Alright, so Leo is kind of a no-brainer when it comes to celebrity watch collectors, seeing as he's one of the silver screen's biggest stars as well as Tag Heuer's long-time ambassador. But what you probably didn't know is that DiCaprio so loves his collection to the point that his own watches had a starring role in his movies. Each of the above-mentioned timepieces has been worn by the Oscar-winning actor before: The Tag Heuer and Rolex appeared in Martin Scorsese's Wolf of Wall Street, the Breitling Chrono Avenger for Blood Diamond, and DiCaprio also sported a classic Raymond Weil piece in his portrayal of Jay Gatsby in The Great Gatsby.

WHO: Jay-Z
NOTABLE TIMEPIECES: Audemars Piguet Royal Oak Offshore, Richard Mille RM027, Hublot Big Bang
Celebrity watch collectors Jay-Z

One half of the world's most famous power couple, the rapper turned multi-hyphenate businessman is a loyal fan of luxury labels and the same devotion extends to his choice of timepieces. An avid collector of the finer things in life, Jay-Z has shored up an impressive haute horlogerie collection and isn't shy about showing it off. His casual everyday wear timepiece is a Rolex Day Date that he owns in both gold and platinum versions, with one of the major pieces in his arsenal being the one-of-a-kind Hublot Big Bang encrusted with 637 diamonds gifted by Beyoncé that rings up a cool five million. Talk about bling.

WHO: Kanye West
NOTABLE TIMEPIECES: Rolex gold Daytona, customised all-black Rolex Submariner, customised gold Tiret

Celebrity watch collectors Kanye West

Notorious for branding his moniker on almost anything he owns — the man's personal tattoo artist has even collaborated with Hublot for a limited edition timepiece — is it any surprise that customised watches are at the top of West's collection? In true extravagant Ye style, the superstar rapper splurged $180,000 for his personalised Tiret timepiece in 18K yellow gold that immortalises his own face (donning his signature shades, no less) upon the dial, created from clusters of white, yellow, brown and black diamonds. This haute horlogerie self-tribute took over five months to complete and also boasts two top-of-the-line Swiss quartz chronographs.

WHO: John Mayer
NOTABLE TIMEPIECES: Patek Philippe 5396G Limited Edition, Patek Philippe Perpetual Calendar, Rolex Emplorer II

Celebrity watch collectors John Mayer

The crooning heartbreaker is as much a connoisseur of women as he is of luxury watches. And though some of the fairer gender likely takes offense at his rakish conduct, put aside his slew of ex-girlfriends and flings and the singer is actually a serious horophile. Not simply purchasing expensive pieces for the sake of impressing the ladies, Mayer takes the time to understand the craftsmanship that goes into a timepiece and his appreciation for horology spans a lengthy 16 years since his first foray into fine watchmaking in 2000. Counting several rare pieces among his watches including a Tiffany & Co. commissioned Patek Philippe and vintage Rolexes, the entirety of his collection is rumoured to be worth something in the range of $20 million.

WHO: Orlando Bloom
NOTABLE TIMEPIECES: Luminor Panerai PAM127, IWC Big Pilot Classic Chronograph, Rolex Milgauss

Celebrity watch collectors Orlando Bloom

Bet you didn't think there would be a dedicated watch collector behind this pretty face. But there was a reason why the English actor and his ex-wife (then girlfriend) Miranda Kerr had their L.A. residence burglarised by the infamous 'Bling Ring' — a group of thieves who targeted the homes of celebrities on a highly publicised year-long crime spree. In part due to Kerr's luxury belongings, the crooks also eyed Bloom's extensive watch collection. A reflection of his refined taste, the star's favourite timepieces include classics from IWC Schauffhausen and Panerai as well as a large collection of Rolex watches, some of which are vintages valued at six-figures, that were among the filched possessions. We can only hope he managed to recover them.

WHO: Jennifer Aniston
NOTABLE TIMEPIECES: Cartier Tank Française, Rolex Presidential, Rolex Datejust

Celebrity watch collectors Jennifer Aniston

Deserving of a honourable mention as one of the handful of female celebrities who knows her horology, Aniston is the proud owner of a vast empire of Rolexes. And while it seems almost every other celebrity has a Rolex or five, the Friends alumni ranks a level higher as she has always preferred the Swiss maison and her dedicated collection is evidence of her loyal following. Often captured in photographs wearing one of her perennial favourites, a men's Gold Rolex President (reportedly bought by ex-boyfriend and fellow horophile John Mayer), the blonde shows the world that her impeccable taste in haute horlogerie is as timeless as she is ageless.