I would say in the US you are upper class if you have a net worth of 100 million or above. Less than that and you don't move in the circles that we think of as upper class.
You might be able to make a case for a "lower upper class" starting around 20 million net worth, which is what you need to enjoy a 1% income without working.
But without 100 million you won't have the influence in the country that the phrase "upper class" connotes.
Want a gut test? If you can't afford to buy a private jet on an impulse you aren't upper class. If owning you own TV station is beyond your means you are not upper class. If you don't have enough money to bankroll a major political campaign you sir are not upper class.
I don't think people appreciate just how rich the wealthy people in America actually are.