> A recent gallup survey says 150M people would move to the US if they could, the UK was a distant second at 45M

Now adjust those numbers to the population of those countries... oh look, the UK all of a sudden came out ahead.

All of these studies comparing numbers usually just boils down to "The US is big". It has been brought up elsewhere that Canada, for example, has more immigrants as a percentage of population. But of course when comparing absolute numbers to the US, it will look like peanuts.

If the reason is the US is big, why would you look at it on a per-capita basis? Maybe adjust for land size? Then the UK would really come out ahead!

Only if immigrants are merely settling empty land. As long as they want to start out as part of society, they'll need jobs, housing and regular infrastructure. My own region is growing nearly as fast as housing can be built. More than 50% of everyone in some cities like Toronto have been in the country for less than 5 years, at any given moment. (Often starting out there, and moving to other parts of Canada later. Still limited by the population capacity of Toronto)

Uh, I guess? It looks like you're making fun of your own original argument at this point. In this case, if you use these numbers as an indicator of demand the UK clearly has greater demand per capita. And per capita is a much better measure since a country with a bigger population can assimilate and/or integrate a larger number of immigrants, thus it can comfortably have a larger immigration demand than a smaller country.

Why does a per-capita number make any sense here?

Because a large country is able to absorb more immigrants than a small country. 150M is 2x the population of the UK, but less than 50% of the US. So it would make sense that the US would have a higher quota than the UK.

Because it is a better proxy for how it will affect society in terms of ability to absorb more people, ranging from tax payer base to things like cost of infrastructure projects to handle the population growth.