In the industry-
The typical "rock cornish hen" is a 21 day old pullet. They are pretty much considered a "co product" and seldom turn a profit by themselves.
42 days (six weeks) of age the as hatched average live weight will be about 5.75 lbs and the average yeild of eviscerated meat will be about 72% This is the average age of broiler chickens slaughtered in the US.
Only males are kept as roasters (guess what happened to their sisters, see "rock cornish hen" above). The average age of a roaster is 56 days and he should weigh about ten pounds at that point. He will yeild a little higher RTC percentage at this point. There are of course larger and smaller roasters for specific market demands.
Backyard chickens can certainly perform this well or better, considering they are often overfed on proteins. Which is not efficient.
Sometimes they will not do as well, usually because of light deprivation, temperature extremes, water quality issues, diseases and other maladies.
94% of the birds placed is considered the minimum number of birds expected to reach the processing plant at 42 days of age.
Yeah, yeah I know I'm all full of it. Your Grandmother did otherwise and some journalist with three hens in his San Francisco back yard says differnt but-
They don't have to make half the bank payments on a farm that has 388,000 broiler chickens at one time- do they.