Facebook shares are being offered to the public for 38 US dollars (£24) in one of the biggest ever US stock flotations.
The social media giant is now valued at more than 100 billion dollars (£66 billion) and stands to reap up to 18.4 billion dollars (£11.6 billion) from the sale of hundreds of millions of shares.
Founded in a Harvard dorm room eight years ago, the social networking site is expected to launch its initial public offering (IPO) on the Nasdaq Stock Market tomorrow.
It was expected prices would set at between 34 and 38 US dollars, meaning demand from investors has been high.
Trading is set to begin under the ticker symbol FB two days after massive interest in the sale prompted the company to boost the number of shares it plans to sell, with 84 million more - worth up to 3.2 billion dollars (£2 billion) - being added to the IPO.
But the entire increase comes from insiders and early investors, so the company will not benefit from the additional sales.
Facebook board members Peter Thiel and James Breyer are among those selling more shares, but founder Mark Zuckerberg is not increasing the number he is selling.
In a filing with the Securities and Exchange Commission, Facebook said current shareholders are now offering approximately 241 million shares, up from about 157 million shares previously.
Investors such as U2 frontman Bono stand to make huge sums, with music magazine NME predicting the singer will become the richest rock star on the planet when the company floats.
Eight years after the concept of Facebook was dreamed up in a Harvard University bedroom, Mr Zuckerberg has become one of the richest people in the US, with 55.8% voting control in the company. The site's revenue last year was 3.7 billion dollars, up from 153 million in 2007, with the majority earned through advertising.