Maybe it's the urban dwelling of the future: studio apartments measuring no more than 300 square feet.

New York City planners believe the tiny units could be the answer to a growing population of singles and two-person households. And in a nation that's becoming increasingly populous and increasingly urbanized -- and where people more frequently are creating a family of one -- such downsizing may not stop here.

Mayor Michael Bloomberg invited developers Monday to propose ways to turn a Manhattan lot into an apartment building filled mostly with what officials are calling "micro-units" -- dwellings complete with a bathroom, built-in kitchenette and enough space for a careful planner to use a foldout bed as both sleeping space and living room.

If the pilot program is successful, a requirement established in 1987 that new city apartments be at least 400 square feet could ultimately be overturned.

City planners envision a future in which the young, the cash-poor and empty nesters flock to such small dwellings, each not much bigger than a dorm room. Where now about one-third of renter households spend more than half their income on rent, it could make housing more affordable than Manhattan's average of $2,000 a month for a studio and $2,700 for a one-bedroom.

Manhattan is the U.S. capital of solo living, with 46.3 percent of households consisting of one person, according to the 2010 census. City officials estimate that 76 percent of residents on the island live alone or with just one other person. They say such households are growing faster around the city than any other type of living situation. The trend is attributed in part to young professionals delaying both marriage and childbearing.

Around the country also, more people are living alone than ever before. The solo living rate rose to almost 27 percent in 2010, according to the census.

In New York City, where long working hours can leave little time for home life, renters often sacrifice square footage to save money. The size of city apartments has been lampooned on television, with at least one sitcom showing characters living -- literally -- in a closet. Some New Yorkers, desperate for storage space, turn their ovens into storage for clothes or other items.

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