Laying hens vary in size and how long they lay through their lives. Generally, they begin laying around 18 weeks of age, but sometimes it will take longer for them to get started. They reach their peak production when they're about a year or 2 old, laying fewer eggs as they age.
Breed Determines Weight
Consider that the ideal weight for a Chihuahua is vastly different for a German shepherd. Just as a dog's target weight depends on his breed, a laying hen's target weight is determined by what kind of chicken she is. The size of laying hens varies widely, according to breed. Henderson's Chicken Breed Chart lists a wide array of chickens, starting as small as 3.5 pounds. The leghorn is a popular hen on the small size, weighing about 4.5 pounds. This lady matures early and regularly produces large white eggs, making her a popular layer. The New Hampshire and Rhode Island hens are also popular, producing brown eggs; these ladies should hit the scales around 6.5 pounds. The 7 pound Minorca produces extra-large eggs and the Orpington, weighing 8 pounds, stands up to cold weather fairly well. The Jersey giant is among the largest laying hens, coming in at 10 pounds. Backyard Chickens notes a 6 pound hen will eat about 3 pounds of feed in a week.