Weight depends on a few things, gender, feed, and of course age and breed. The average hatchery stock breeds won’t be terribly impressive but IMO one young cockerel around 15 weeks old is enough to feed 2-3 adults.
I try to keep track of my own birds I butcher and how much they weighed before and after processing. Today I butchered 3 15 weeks old cockerels who were sons from a BJG and SLW hen fathered by a blue copper maran. Weights were 4lbs 3oz, 4lbs 9oz, and 5lbs (SLW son). After processing they were 2lbs 4oz, 2lbs 9oz, and 3lbs 1oz respectively. This was skinned with necks and wings attached. These birds were broody raised and fed whatever the main flock was getting, 20% chick starter for the first month or so and then layer pellets and layer mash mixed with chick starter for a 17% protein.
Not too long ago I processed 2 12 weeks old cockerels, different moms but same father as above. These were fed meat bird feed (22%) and while I didn’t get before weights they ended up being 2lbs 6oz and 2lbs 4oz plucked. Compared to the 3 I butchered today I would say they were nearly the same size despite the 3 week age difference.
With 2 other 19 week old cockerels, a RIR and a large fowl mutt they dressed out (plucked) at 4 and 6lbs. So simply put, it varies greatly depending on breed, breeding stock, age and to a somewhat lesser extent, feed.