How much living space would you get if you only spend 30% of your monthly income on rental housing in Santa Rosa, Petaluma and Rohnert Park? Not enough to pay for the average-sized apartment.

In fact, 30% of the median monthly income in Rohnert Park — about $5,373 a month — would get you 686 square feet of living space. That’s about 83% of the city’s average apartment size of 833 square feet, according to a study released this week by RENTCafe, a nationwide apartment search website. Personal finance experts say spending 30% of monthly income on housing is prudent.

RENTCafe, which is owned by global software company Yardi Systems, calculated that a median monthly income of $5,746 in Santa Rosa gets you about 750 square feet, or 90% of the of the city’s average apartment size of 831 square feet.

Meanwhile, a median income of $7,270 in Petaluma gets you an 869-square-foot apartment, or 92% of the city’s average apartment size of 940 square feet.

The living space study, written by Sanziana Bona of RENTCafe, used median income data from the U.S. Census Bureau’s 2017 American Community Survey adjusted for inflation and Yardi’s apartment data.

Bona said that in Santa Rosa renters’ median household income increased by about 10% from 2013 to 2017. But the “shares of high-income and upper middle-class renters saw significant growth, while the percentage of low-income earners actually decreased in five years,” Bona said Wednesday in an email.

“These trends might explain why a median renter in Santa Rosa can afford (83%) of the average apartment size without being rent-burdened,” she said.

Bona said those who live in large metropolitan areas only can rent a limited amount of space on a strict budget, even those with higher incomes. For example, in Brooklyn, 30% of the median monthly income will only get you 265 square feet of space, in a city where the average apartment size is 697 square feet.

In Manhattan, that share of median income gets you 290 square feet and in Oakland you get 340 square feet. Consequently, many households end up spending more than the 30% benchmark, a general rule that is more idealistic than realistic.

“Large cities, especially the ones attractive in terms of jobs and incomes, are becoming more populous, which pushes the demand up,” Bona said.

You can view RENT Cafe’s national living space report at https://www.rentcafe.com/blog/apartmentliving.