Billionaires' fortunes have doubled since financial crisis

Stock4B | Getty Images

The global financial crisis was good for billionaires.

The combined fortune of the world's billionaires has more than doubled, to $6.5 trillion, from $3.1 trillion in 2009, according to Wealth-X and UBS Global Billionaire Census 2013. Their fortunes have grown by $226 billion in the past year alone.

The group's number also grew by 810 during the period, to 2,170.

(Read more: Asia shines as billionaire hot spot in 2013)

Their total wealth is now larger than the GDP of any country except that of the United States and China, and could fund the U.S. budget deficit until 2024, according to the report.

What else do we know about these billionaires?

Most are entrepreneurial men, and most of their money comes from private companies. They have an average of four homes and 2.1 kids, according to the report.

Of course, talking about the average billionaire is like talking about the average celebrity. It's tough to generalize.

Sixty percent of the billionaires are self-made, according to the report, while 20 percent inherited most of their wealth and 20 percent inherited a portion of it. This is roughly in line with the inheritance/self-made ratio of the Forbes list.

(Read more: Calls to raise taxes for the rich are growing)

The report said 87 percent of the world's billionaires are men. Among the women, only 17 percent made their money themselves, with most deriving it from inheritance.

Marriage plays a key role in building wealth, however: 86 percent of billionaires are married (though the report doesn't specify the number of marriages per capita).

"Spouses often play a pivotal role in the success of their partners," it said.

Billionaires like to keep their families relatively small, with an average of 2.1 kids, though about a third of them have three or more.

New York is the top city on the planet for billionaires, with 96. But billionaires own an average of four homes and $78 million in real estate. (Such holdings represent only 2.6 percent of the average billionaire's net worth.)

(Read more: Wealthy steer from yachts despite higher stocks)

They are highly mobile. Less than one-quarter live in the city their business is headquartered in, while the same percentage don't even live in the same country as their primary business.

The average billionaire spends $22 million on yachts, $16 million on private planes and $14 million on art.

—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.

Watch "Secret Lives of the Super Rich," an all-new series airing Wednesdays at 9 p.m. ET/PT. http://superrich.cnbc.com