Broiler refers to chickens that have not been bred within three months (slightly different according to different breeds, at least less than one month).
Common chickens, when they grow up, should be castrated cocks weighing about 2-5 kg, which can grow bigger. Some 7-8 kg may be calculated according to 2 kg equivalent to 1 kg, so chickens are generally above 1 kg and below 5 kg.