His argument, in generously broad strokes, was that the system was overwhelmed, a function of a surge in migrants seeking entry to the country and that many of them seek asylum upon arrival. But Trump, never one to leave a bole un-hypered, raised the stakes.

“Our country is full, our area is full, the sector is full,” Trump added. “We can’t take any more. Sorry. Can’t have it. So turn around. That’s the way it is.”

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Our country is full! That’s a remarkable phrase that will no doubt alarm pregnant women the country over. Sorry, ladies! You need to either head to Canada or the ocean because that baby simply can’t fit anywhere within our great nation’s boundaries.

This is a joke (for now). Look out of any nearby window and, assuming that you’re not currently living in a house set in the middle of a Jay-Z concert, you’ll probably notice a bit of space in which someone could stand. Maybe even stretch out for a nap.

Clearly we’re not full full. But Trump’s phrasing nonetheless raises an interesting question. If we wanted to, how many more people could we squeeze into the United States?

Filling empty houses

We will start by noting that, on any given day, there are a lot of existing homes that are sitting vacant.

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The Census Bureau tracks this. Last year, there were about 3.4 million rental properties that were vacant, along with about 9.8 million year-round homes that sat empty and another 4.2 million empty seasonal properties — lake houses and ski chalets and such.

Let’s assume that we fill all of those up, meeting the national average of 2.6 people per household. (Don’t spend a lot of time thinking about how these millions of homes will each contain an object that constitutes slightly more than half a person.)

With that baseline, we have the ability to immediately house 8.8 million people in those rental properties, 25.5 million in the year-round houses and 10.9 million vacation-home people who will suffer through very cold winters or very hot summers. In total, we still have space for a bit over 45 million more people before America’s really full.

Matching the most densely populated country in the world

At least if we only consider existing housing stock. We could obviously fit a lot more people if we also built a lot more housing. After all, the United States is one of the less densely populated countries in the world, with slightly fewer people per square mile than Venezuela.

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What if the United States were instead as densely packed as, say, the Gulf nation of Bahrain? Bahrain is the most densely packed country that isn’t also a city, with 5,582 people per square mile. That’s not as horrible as it sounds; New York City is about five times as densely packed.

So how many people could we fit if we built out the United States to that same density? There are about 3.5 million square miles in the country, meaning that we could have a total population of 19.7 billion people without becoming the mostly densely populated country in the world. In other words, everyone in the world could move here and then spontaneously clone themselves and the United States would still be more spacious than Bahrain.

Of course we already have 327 million people living here, so we really only have enough space for another 19.4 billion people.

Literally cramming as many people as possible on every square inch

Again, though, that’s setting a standard for habitation that isn’t exactly pushing the envelope. What if, instead of housing everyone, we wiped the entire surface of the United States clean and simply packed in as many people as we possibly could?

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Believe it or not, we’ve actually considered this question before, at least for a limited area. In 2016, we speculated about how many people could actually fit in Times Square on New Year’s Eve, given the regular claims that 14 bajillion people watched the ball drop. To answer the question (about 120,000), we spoke with G. Keith Still, professor of crowd science at Manchester Metropolitan University in Britain. Still provided us with the results of his research which, at one point, included tying together a group of men to see how closely people could stand and still walk as a group.

Still’s baseline for manageability is five people per square meter, a density that looks like this.

Why five?

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“When you exceed five, both the psychological and physical limits are reached,” Still told us. “It begins to feel cramped and the risk of trips, slips, falls and crowd surges increases exponentially above six or seven per square meter.”

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So, in the interest of public safety, let’s set our upper limit on how densely packed the New United States will be is at five people for each of the country’s ... 9.2 trillion square meters.

Meaning that we could eventually see a total of 45.8 trillion people standing on the bare earth of this refurbished nation. How many people is that? Well, about 417 times the total population of humanity over the entire course of history. So just take everyone who’s ever lived, clone them 417 times, and welcome them across the border. (Please do not clone Adolf Hitler or Pol Pot, among others.)