New York wants to spend at least $9 billion to build new jails in four boroughs, and it’s also spending billions of dollars to protect us from climate change.

Yet even a year into Mayor Adams’s “Get stuff done” regime, we can’t build five public toilets for less than $5.3 million, way higher than the cost other cities have spent.

The tale of the Portland Loos, first reported in The City on Monday, is particularly instructive in how much it costs to build anything — if we even can build anything — in New York.

In most construction projects, the city lumps the cost of materials, the cost of labor and the cost of management all in together, making it hard to figure out what is what.

In the jails venture, for example, we have no idea how much the city will spend on concrete and steel vs. how much it will spend on construction labor and design consultants.

But with the Portland Loo, conveniently, we know exactly how much the physical product costs.

Whether you are New York or Seattle, the company that makes them, Madden Fabrication, sells them for about $185,000 apiece: $185,000 times five is $925,000.

Meaning we’re spending nearly $4.4 million on … what? How do we get to $875,000 apiece just to install a single toilet, after the toilet’s physical cost?

Other expensive cities have done better.

A decade ago, San Diego spent the equivalent of $358,000 in today’s dollars to install a Portland Loo toilet.

That’s less than half what we’ll spend — even though in San Diego, just like here, the city spent extra to ensure the toilets would meet strict building codes, including earthquake standards.

Kodiak, Alaska, spent about $200,000 apiece to install its Portland Loos just last year.

Terrace, Canada, says it will cost about $70,000 (in US dollars) to install theirs this year.

Sacramento estimates it costs less than $200,000 to install the loos.

This is a wide range — but no city comes close to New York’s nearly seven-figure cost to do what is straightforward work: hook up a pre-fabbed unit to water, sewer and power.

One big issue is the state’s prevailing-wage law. City contractors will do the sewer and other hookup work.

Under state law, contractors must pay a basic laborer $94 an hour in pay and benefits, plus overtime.

There are also costs to manage the project — which rise the longer the project takes.

Since New York doesn’t expect to install these toilets for at least 15 months, multiple people at the parks department will have to shepherd the project through the public-design commission and five community boards.

These, too, are full-time, well-paid jobs.

These same costs are what make it too expensive to build something that is nicer than the Portland Loo, a public toilet that is so bare-bones it’s easily confused with a prison toilet. (In fact, that is the point of the Portland Loo, to discourage people from lingering — the water spout, not even a sink, is actually outside.)

There is no mystery to this: After physical parts and transportation, there is nothing left but labor and management.

It’s not asking too much to build real restrooms in more well-used parks, but we just can’t: They cost $4 million to build even before the pandemic, after which inflation pushed up overall prices.

Adams understandably wants to leave a physical mark on the city.

And the jails aside, he’s starting with admirably low-key projects: Maybe we don’t need massive mega-projects for a while, but we could use some bathrooms and nicer streets.

A good place for Adams to demonstrate he can start to control costs is the bathrooms.

Nicole Gelinas is a contributing editor to the Manhattan Institute’s City Journal.