Millennials can absolutely afford to buy homes -- as long as they don't mind living in a house smaller than a toolshed.

In over half of the biggest U.S. cities, the typical millennial can't afford a 1,000 square-foot home , according to a recent report. SmartAsset, a tech company that offers tools to make financial decisions, used their home affordability calculator to analyze median income and net worth of people under age 35. It then compared the results to interest rates and the down payment needed to buy a home in the largest 23 cities.

The calculator, which is supposed to help a potential homebuyer determine what size and cost they can afford, might be useful for, say, a middle-class family trying to decide if they have the resources to buy a house with a spare bedroom. But the results can get absurd in many of the largest cities.

In Denver, Los Angeles, Philadelphia and Washington, D.C., millennials can afford a house that measures less than 500 square feet. In New York, that number is 165 square feet. In San Francisco, it's 135 square feet -- smaller than the city's parking spaces , as Fortune points out.

Millennials could afford the biggest houses in Detroit and Memphis, and Chicago is more reasonable than the coastal cities it competes with.

The idea of a 200-square-foot house would make many people balk, but theres been growing interest in micro-housing units , with developments -- mainly apartment buildings -- underway or completed in most of the priciest cities . And theres at least one pitch to build affordable small homes specifically for millennials , though its unclear if the idea, floated by a councilman in Washington, is viable or even legal.

But its not like these units are plentiful: houses are actually getting larger each year. In 2014, the median size for new single-family houses was 2,453 square feet, according to a report from the U.S. Census Bureau. Apartment units intended for sale are much smaller, but just 14 percent of apartments built for sale in 2015 were under 1,000 square feet.

The SmartAsset findings -- which don't look at small cities and suburban areas, where homes are likely to be more affordable -- help explain why fewer people in their 20s and early 30s are buying houses than a decade ago. The flippant explanation has often been that millennials are putting off adulthood, content to camp out in their parents basement or curl up under the desk at their coworking space rather than grow up and get a mortgage.