The length of the growing cycle depends on the market for which the bird is being raised. Most chickens are ready for market when they weigh around two kg. It takes 38-40 days for chickens to reach this weight. You may see chickens in other sizes too. A Cornish hen weighs between 1 and 1.1 kg at live weight and is ready for market in 25 days. And a roaster, which is grown in 45 days, weighs about 3 kg.
Check out www.wfs.ca for typical target weights.