How low does oil level get before warning comes on?



We have a 2010 ML350 Bluetec, and I have been monitoring it's oil consumption. I have another thread here that talks more about that, but I'm currently waiting for the low oil light to come on and curious if anybody knows if it's 2 quarts, 2.5, 3?
I checked the oil the other day and it's near the bottom, but still visible. But mostly I'm worried that if that sensor dies I will run it too low.
Cheers,
Ian








Most of the engines have 2l between Min and Max mark, but that is not standardized.


