I’ve seen countless online indications that roasting a whole chicken calls for a bird of 3-3.5lbs (circa 1.5kg). Problem is: in my USA environment, it is impossible to find a bird much less than 5lbs. (2.7kg). Where you are, is there any such thing as a 3lb bird?
I’ve noted that chickens here in the USA midwest are labelled as “fryers” or “roasters,” but in fact, both of them weigh in about the same 5lbs. Something odd is going on, I think.