For the first time being a billionaire isn't enough to guarantee you a place on the Forbes magazine annual rich list.
Microsoft founder Bill Gates remains the richest person in America for the 14th year in a row, followed by investor Warren Buffett.
The pair's fortunes each grew by $6 billion ($A6.9 billion) in the past year, according to Forbes, with Mr Gates' fortune now at $59 billion ($A67 billion) and Mr Buffett $52 billion ($A59 billion).
Mr Buffett has pledged 85 percent of his net worth to the Bill and Melinda Gates Foundation and family charities.
Casino magnate Sheldon Adelson ($A32 billion), head of Las Vegas Sands Corp, and software tycoon Larry Ellison ($A29 billion), chief executive of Oracle Corp, remain at No 3 and No 4 on the 25th annual ranking of 400 rich Americans, which now requires a minimum net worth of $A1.49 billion for inclusion.
"The collective net worth of those listed on the 400 this year rose $290 billion ($A333 billion) to $1.54 trillion ($A1.77 trillion) ," Forbes said. "Despite market jitters, nearly half of the 45 new members come from hedge fund and private equity investments."
Waltons miss out
For the first time since 1989 there are no members of the Walton family, descendants of Wal-Mart Stores Inc founder Sam Walton, in the top 10. Four members – Jim, Christy, Robson and Alice – slipped to 12th and 15th place.
The Waltons were displaced by Google co-founders Sergey Brin and Larry Page, who came in at No 5 with fortunes of $18.5 billion ($A21.31 billion), and brothers Charles and David Koch, who run Koch Industries, the world's second largest private company, and are each valued at $17 billion ($A19.58 billion), earning them 9th place.
Investor Kirk Kerkorian was the biggest gainer on the list, his fortune rising by more than $9 billion ($A10.37 billion) in the past year to $18 billion ($A20.7 billion). He debuted in the top 10 at No 7 — up from No 26 last year.
Michael Dell, chief executive of Dell Inc, the world's second-largest PC maker, was No 8 on the list with a fortune of $17.2 billion ($A19.82 billion).
Of the top 400 richest Americans, Forbes said 270 were entirely self-made, 74 inherited their wealth and 39 are women. There were 82 American billionaires who did not make the list.
The youngest member, and new to the list, is 33-year-old hedge fund manager John Arnold, who came in at No 317 with a $1.5 billion ($A1.72 billion) wealth, while the oldest is 98-year-old John Simplot, valued at $3.6 billion ($A4.14 billion) and No 214 on the list.