According to Sunni, what is the gauge that shows it is mandatory for a Muslim to go to Haj (Wajib-al-Haj)?

I have heard that going to Haj is not Wajib(mandatory) for those people who cannot afford to pay the expense of this trip. But my question is that how we can recognize if it is Wajib for us to go to Haj? in fact, is there any specific factor(s) which show it ? for instance, Will it be Wajib for us if we can provide its ticket expense by selling our gold or car and so on? (I am looking for the view of Sunni)