Vogue

Vogue magazine's key issue of the year - the September book - will feature pop star Lady Gaga on the cover. As if that weren't enough, the issue will be remembered also for being the magazine's biggest ever.

A spokesperson for the magazine said next month's issue will contain 658 ads, representing a 14 percent growth over last year's issue.

To mark the magazine's record-breaking September issue, the publication on Friday will launch a Facebook contest asking readers to guess the page count.

Photos: The many faces and moments of Lady Gaga

One-hundred readers who guess closest to the actual number will win Vogue's new Editor's Eye book, complete with autographs by Vogue editors. The actual page count will be revealed on Saturday.

This will be Gaga's second Vogue cover. The first, in March 2011, was a huge hit, going on to become the magazine's second biggest-seller of that year.