How Britney Spears' 3.5-Carat Engagement Ring Stacks Up To Beyonce, Katy Perry, Mariah Carey, and Christina Aguilera's

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Britney Spears accepted her long-time beau and former agent Jason Trawick's marriage proposal this week. She and her groom-to-be celebrated their engagement at his 40th birthday party at Planet Hollywood Resort and Casino in Las Vegas. Brit told her Twitter fans she was 'still glowing' after he proposed. And she certainly looked radiant, flashing her 3.5-carat diamond sparkler designed by Neil Lane for the cameras.

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There's been no word on cost of the ring. And we're not saying it's not a pretty ring because it is. But Britney is (or was) the Princess of Pop. So how does Spear's engagement ring stack up -- carat-wise -- to other famous females?

 According to the Celebrity Bride Guide, Beyonce got an 18-carat diamond ring by Lorraine Schwartz diamond ring from Jay-Z that's worth more than $5 million. Musical diva Mariah Carey younger hubby Nick Cannon gave her a Jacob and Co. 17-carat diamond worth is estimated at $2.5 million. Edgy jeweler Stephen Webster designed Britney's Mouskateer buddy Christina Aguilera's 5-carat diamond ring bought by her manager Jordan Bratman. And Katy Perry's sporting a 12-13-carat round brilliant cut diamond ring that cost her hubby Russell Brand a reported $1.3 million.

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The Duchess of Cambridge Kate Middleton is wearing Princess Diana's ring, an 18 -carat oval sapphire that originally cost $65 grand. But reality TV royalty Kim Kardashian tops that with  Kris Humphries' 20.5-carat Lorraine Schwartz engagement ring. The ring reportedly cost Humphries $2 million, is probably worth $3 mill but may be devalued to just $1 mill. Oh, and it looks like Kim's gonna keep it. Her sister Khloe Kardashian loves her 9-carat diamond ring from Vartan's Fine Jewelry, via Lamar Odom.

Even Hollywood actresses get more carats than Britney. Couch-hopping Tom Cruise wowed Katie Holmes with a 5-carat Edwardian style diamond solitaire ring with pave detail on top of the Eiffel Tower in Paris. Estimated cost of the ring? Over $250,000. Getting engaged on the Eiffel Tower to one of the biggest movie stars in the universe? Priceless.

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Reese Witherspoon's engagement ring is a rare 4-carat Ashoka diamond engagement designed by William Goldberg that cost an estimated $250,000. Jennifer Garner accepted Ben Affleck's 4.5 carat cushion Harry Winston ring. Even Jennifer Aniston got a ring estimated at $500,000 from Brad Pitt. But Scarlett Johansson only got a $30,000 3-carat diamond solitaire from Ryan Reynolds, who could probably afford more carats now, after his Green Lantern action hero paycheck.

While Aquilera, Aniston and Johnasson are no longer married, we feel it's necessary to point out that the size of your rock has absolutely nothing to do with your marriage hitting the rocks. Oh, wait. Maybe it does.