You need to make $142,000 a year to buy a typical house in San Francisco

You need to make only $31,716 a year to buy a home in Pittsburgh. In San Francisco, you need more than four times that.

That’s what mortgage information site HSH found when it studied home prices in 27 major US metro areas. The figures assume a 20 percent down payment and that buyers spend 28 percent of their income on housing costs. They also incorporate property tax estimates and make allowances for homeowner’s insurance. Here’s a look at HSH’s estimates for how much people would need to earn annually to buy the median home in a range of metro areas:

These figures aren’t hard lines — they make a lot of assumptions about how much people will spend. And, more important, not everyone is trying to buy the median home. Rather, these are gauges of home affordability in different US cities, and the big takeaway here is that the gauge swings wildly from one place to another.

High demand and high incomes help push up home prices in some cities — lots of people want to live in Washington and New York, and those metro areas also are home to lots of high-paying jobs.

But that’s only part of it. Bad policy can exacerbate the problem. One reason purchasing a home in San Francisco is so hard is that strict housing laws have created a housing shortage in that city, Tim Lee wrote last year. That has pushed middle- and low-income people out of the city while Silicon Valley wealth moves in. Similarly, Washington, DC’s building-height restriction has helped send the city’s housing prices into the stratosphere.

[h/t Wonkblog’s Ana Swanson]