The 9th Circuit’s per curiam opinion in Hawaii v. Trump begins with this estimate:
For the third time, we are called upon to assess the legality of the President’s efforts to bar over 150 million nationals of six designated countries from entering the United States or being issued immigrant visas that they would ordinarily be qualified to receive.
The court reaches this number by adding the populations of six predominantly-Muslim nations that are subject to the travel ban. According to the CIA World Factbook, the estimate is closer to 158 million: Chad (12,075,985), Iran (82,021,564), Libya (6,653,210), Somalia (11,031,386), Syria (18,028,549), and Yemen (28,036,829).
The 9th Circuit’s analysis is premised on every single person in these nations attempting to enter the United States, or seeking an immigrant visa.
This estimate is not even plausibly realistic. In 2016 for example, the United States issued 25,578 immigrant and 47,816 non-immigrant visas to aliens from these six nations, totaling 73,394 visas. As noted in this spreadsheet, only a tiny percentage of the population of these nations ever received a visa to enter the United States. Indeed, the actual numbers are even smaller, because only certain visa categories are subject to the travel ban. More people no doubt sought to enter the United States in 2016, but they were denied visas by the Obama administration.
When the Supreme Court reaches this issue, I hope they do not repeat this bizarre 150 Million number. It has rhetorical force, but lacks any grounding in actual immigration patterns from these countries. The real number is likely less than 100,000.