a77 resolution

I'm not talking about the distance to the subject, I'm talking about the width of the subject. If I compose a photo so that an object of 6*4 m fits exactly in the viewfinder, what is the least distance between two points of the object that I can see if I later magnify that photo? Should it be 1 mm because the resolution is 6000*4000 or is it 2 mm or more?

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