If you buy a whole chicken in the supermarket it is defeathered, without head and feet and with the inner organs removed (sometimes you get some organs in a bag but I'm going to ignore that for this question). What I would like to know is how much, in terms of weight of a living chicken is a whole supermarket chicken? How much weight are the various pieces that are removed? If this makes a difference, assume the supermarket chicken weighs 1.5 kgs (a little over 3 pounds).
Broiler chickens, at least in the US, are bred to grow quickly. They are usually slaughtered when then weigh about 4 pounds, which is at about 7 to 9 weeks. In general, a grocery store broiler weighs about 3 to 3.5 pounds. As the comments above suggest, this is a very general response. It would be difficult to be more accurate.