At least how the NY Times defines it. They have a calculator at:
I'm not saying I agree with all of the parameters of this calculator, especially since the NY Times itself admits that the 4 parameters used to measure your status are just some of the "more influential" characteristics that affect class, by they are certainly not the only ones.
Anyhoo, yes I am aware that I would be l labeled as "middle class." I consider it a compliment, since 5 years ago I was in the depths of poverty by the same standard. Within the next 10 years, I plan to ascend to the "top fifth" category, where my progress and hard work will be demonized, scrutinized, and stolen by those who don't feel they are willing or capable to follow the same path of progression that I did, for whatever reason.
I believe that 'class' is an ancient notion. There is no existing social class today. Globalization has blurred all disinction. Although people still possess different amounts of wealth, they are not conscious of the divide in society. There are no values common to the aristocracy. Everybody is approximatly the same and most people have similar life-opportunities.