How much does it take to feel wealthy these days? For many millionaires, it’s about $7.5 million, according to a survey by Fidelity Investments.

"Wealth is relative, and to some extent the more you have the more you realize how much more you need," Sanjiv Mirchandani, president of National Financial, a subsidiary of Boston-based Fidelity that provides clearing and custody services to broker-dealers, said before the survey’s release yesterday.

The more than 1,000 households surveyed had an average of $3.5 million in investable assets. About 42 percent said they don’t feel wealthy, saying they would need about $7.5 million to feel rich. The 58 percent of respondents who said they do feel wealthy were younger on average and have a greater number of remaining years in the work force, Mirchandani said.

A 65-year-old millionaire is "looking at potentially the loss of a paycheck as they retire, and 30 years in retirement, with inflation on the horizon," Mirchandani said. "So they kind of go ‘Well, $3.5 million, $4 million, isn’t what I thought it would be. I’d like to have more.’"

There are about 5.5 million U.S. households with at least $1 million in assets, or about 5 percent of the population. Millionaires control 56 percent of the country’s wealth, according to Fidelity, which is the second-largest U.S. mutual-fund company after Vanguard Group Inc. Household wealth was $56.8 trillion at the end of 2010, according to the Federal Reserve.

The survey found millionaires’ outlook for the future is the most positive it’s been in at least four years.

"They’re beginning to feel that perhaps we’re turning the corner on a more consistent basis," said George Walper Jr., president of Chicago-based Spectrem Group, a consulting firm that tracks attitudes among millionaires.

About 56 percent of registered investment advisers, who manage or advise individual investors’ money, are bullish on the stock market’s prospects over the next six months, according to a January survey by San Francisco-based Charles Schwab Corp. Of the advisers surveyed, 23 percent said they’re providing reassurance to their clients about reaching their investment goals, down from 49 percent in January 2009.

About 83 percent of millionaires surveyed by Fidelity said the financial crisis didn’t shake their confidence in investing, and 43 percent said they plan to invest more money in stocks over the next 12 months. A majority said a goal is preservation of capital, rather than growth.

"They’re still fairly conservative in terms of what they’ll buy," Mirchandani said.

Millionaires planned to give $38,000 on average to charity in 2010, up from $36,000 in 2009, the Fidelity survey said.

The asset-management firm hired New York-based Northstar Research Partners to survey 1,011 households with at least $1 million in investable assets via the Internet during October 2010.