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The 20,000-square-foot Star Island, Fl.- mansion of 'Real Housewives of Miami' star Lisa Hochstein and her husband Lenny.
The 20,000-square-foot Star Island, Fl.- mansion of 'Real Housewives of Miami' star Lisa Hochstein and her husband Lenny.
Thibault Monnier—Celebrity Home Photos/Newscom

Think most millennials wouldn't be caught dead buying their parents' hulking 10,000-square-foot McMansions? You're right -- they want 20,000 square feet instead.

About 40% of wealthy younger buyers -- those aged 25 to 49 -- told real estate broker Luxury Portfolio International they hope to own a house larger than 10,000 square feet, long considered the upper range for McMansions, in a survey published this week. Nearly a quarter -- 23% -- said they want a home 20,000 square feet or larger.

If you didn't think people bought houses that big, you're kind of right. The average U.S. home size was about 2,400 square feet in 2016, according to government data. The survey's respondents, who were an average of 37 years old with assets of $1 million or more, want a house about eight times that size.

Need help picturing that? Think four times the size of Kendall Jenner's $8.55 million Los Angeles spread or about the size of Taylor Swift's Rhode Island estate and DJ Khaled's Florida mansion -- combined.

It is, however, only two-thirds the size of the Taj Mahal and a little under half the size of the White House.

In this May 27, 2013 photo, people walk past a house owned by Taylor Swift in the village of Watch Hill in Westerly, R.I.
Dave Collins—Dave Collins/AP/REX/Shutterstock

While 20,000-square-foot homes do exist, actually purchasing one won't be easy, even for the survey's young buyers with average assets worth $4.7 million.

There’s a lone single-family home measuring 20,000 square feet on the market in Manhattan -- for $50 million-- and only a handful of similar listings in Los Angeles, ranging in price from $14 million to more than $70 million. Since the majority of these prospective buyers say they prefer urban settings, the pickings are slim.

Other particular preferences might reduce their choices even further. Young buyers don't necessarily have strong architectural preferences, according to the survey. Victorian and modern-style houses out-polled Tudor and Georgian ones, but only a slim margin. They are picky when it comes to amenities, however. Outdoor patios or terraces, commercial-grade kitchen appliances and a spa, Jacuzzi or hot tub are all among features survey respondents told Luxury Portfolio International they considered "essential."

Of course, older buyers weren't immune to visions on real estate grandeur, either. About 10% of those 50 older said they too hoped to own homes that were 10,000 square feet or larger. But boomers seemed to largely be in downsizing mode. The greatest share of respondents age 50 and above -- 38% -- agreed that their next home purchase would fall between 3,000 and 5,000 square feet, while the second-largest group preferred 2,000- to 3,000-square-foot homes.