No, they’re not, but they’re mostly considered “American” in common parlance.  For example, if you’re counting people who are natural-born or naturalized US citizens and who aren’t illegal immigrants, then the US population is

“265 million and Puerto Ricans would still only be around 1.2% of the population”

and that number would only increase if you count other Americans like those born in US territories and military members.  Of course, this is just common parlance, and usually in the US it doesn’t really matter much.  In some ways you’d need to be extra pedantic to realize that Puerto Ricans are considered Americans.  A lot of people don’t think about it at all.  A lot of people think Puerto Ricans are foreigners and legal immigrants, or as illegals, and that people from Puerto Rico aren’t “real Americans”.
assistant
That’s correct.  Let me explain.  The US has a lot of laws about citizenship and immigration.  To be considered a citizen, you must be born in the US or have a parent that’s a citizen.  But if you’re born in another country, you can have a parent that’s a citizen, and apply for US citizenship.  What that means is that if you’re born in Puerto Rico, you’re also eligible to apply for US citizenship, since the place of birth is Puerto Rico, not the US.  So if you’re a person with a parent who’s a US citizen, you can apply for US citizenship by proving that you’re a “citizen of the United States” which is defined by the Immigration and Nationality Act.  If you’re able to prove that, then you’re a US citizen.  Does that make sense?
assistant
Why are Puerto Ricans considered Americans?
user
Actually that’s not true.  Puerto Ricans have US citizenship, but they’re considered “foreigners” in the US because they’re not born on US soil.  Is this what you were asking?
assistant
Oh, I thought so. So they aren't full on Americans.
user