Is UCLA or Stanford more selective for undergraduate admissions?

The biggest practical difference is that Stanford is considered markedly harder to get into overall, while UCLA is also extremely competitive but admits from a much larger applicant pool and enrolls a much bigger undergraduate class. In everyday admissions terms, Stanford sits in the very top tier of selectivity nationally, and UCLA, while highly selective, is not usually viewed at that same level of difficulty. For an applicant trying to gauge odds realistically, Stanford is the more selective school.

Part of that comes from scale and process. Stanford has a smaller undergraduate population and far fewer available seats relative to demand, so admission is exceptionally constrained. UCLA receives enormous interest too, but as a large public university it enrolls many more undergraduates, which changes the level of scarcity even though competition remains intense.

The applicant pools also overlap somewhat but are not identical. Stanford tends to attract a very concentrated pool of students with top academic records, strong extracurricular distinction, and national or international-level accomplishments. UCLA attracts many outstanding applicants as well, especially from California, but the overall admissions landscape is broader because of its public mission and larger class size.

So if the question is simply which school is more selective for undergraduate admission, the answer is Stanford. UCLA is still one of the most competitive public universities in the country, but Stanford is more difficult to enter overall.