Here are three different breeds of chicken, raised on the exact same diet: 
The one on the left is a breed from 1957. The middle one is a 1978 breed. And the one on the right is a commercial 2005 breed called the Ross 308 broiler. They’re all the same age. And the modern breed is much, much, much larger.
In just 50 years or so, chickens have been bred to be much bigger. The above comes from a study done by researchers at the University of Alberta, Canada, who raised three breeds of chickens from different eras in the exact same way and measured how much they ate and how they grew. This allowed them to see the genetic differences between the breeds without influences from other factors like food or antibiotic use. They recently published their results in Poultry Science.
Chickens come in a wide range of sizes, from tiny bantams to giant heavyweight breeds. But just how big is a chicken? The size depends on factors like breed, sex, and age. This guide will provide a complete overview of chicken sizes to help you understand how big your chickens will get.
Factors Affecting Chicken Size
Several key factors influence the final size a chicken reaches
Breed
Chicken breeds have been selectively bred for different traits over hundreds of years. Some breeds have been bred specifically for small or large size. The breed has the biggest impact on full grown size.
Sex
Male chickens (roosters) are usually quite a bit larger than females (hens) of the same breed. This sexual dimorphism is common in bird species.
Age
Chickens grow rapidly in their first few months, reaching adult size between 5-7 months old depending on breed. Weight continues to increase slowly after this time.
Environment
Factors like nutrition and living conditions can affect growth rates, Chickens raised in spacious outdoor runs tend to grow larger than confined chickens
Chicken Weight By Breed
Here are the average adult weights for popular chicken breeds
- Large Breeds:
- Brahmas: Hens 8 lbs, Roosters 10 lbs
- Cochins: Hens 8.5 lbs, Roosters 11 lbs
- Orpingtons: Hens 8 lbs, Roosters 10 lbs
- Standard Breeds:
- Rhode Island Reds: Hens 6.5 lbs, Roosters 8.5 lbs
- Plymouth Rocks: Hens 7.5 lbs, Roosters 8.5 lbs
- Australorps: Hens 8 lbs, Roosters 10 lbs
- Bantam Breeds:
- Silkie Bantams: Hens 1.5 lbs, Roosters 2.5 lbs
- Japanese Bantams: Hens 1.1 lbs, Roosters 1.3 lbs
As you can see, there is significant variation among breeds. Large fowl breeds are 3-4 times heavier than bantam breeds.
How to Estimate Mature Chicken Size
If you’re getting chicks, you can estimate their full grown size:
- Weigh chicks at 1 week old. Large breeds weigh 25-40g, bantams weigh 10-25g.
- Multiply 1 week weight by 50-60x for large breeds, or 35-40x for bantams.
- For example, a large breed chick weighing 30g would grow to 1.5 to 1.8 kg (3.3 to 4 lb).
This method provides a rough estimate only, but can help predict chicken coop needs.
How Fast Do Chickens Grow?
Chick growth occurs most rapidly in the first 3 months of life:
- At 1 month old, large breed chicks weigh 0.5-0.9 kg (1-2 lb)
- At 2 months they reach 1.1-1.8 kg (2.5-4 lb)
- By 3 months they are 1.4-2.2 kg (3-5 lb)
After this point, weight gain slows significantly. By 5 months, most of the length and width of the body are set.
Chicken Size By Age
Here is a guide to chicken sizes by age for standard large breeds:
- Day old chicks: 25-40g
- 4 weeks: 340-850g
- 8 weeks: 1-1.5 kg
- 5 months: Full adult weight
So you can expect very rapid growth in the first 2 months, then a slowdown as they finish maturing.
How Much Space Do Chickens Need?
How much space a chicken coop or run needs depends on the size of the birds. Here are the general recommendations:
- Large breeds:
- Coop space: 8 sq ft per bird
- Run space: 15 sq ft per bird
- Standard breeds:
- Coop space: 4 sq ft per bird
- Run space: 8 sq ft per bird
- Bantams:
- Coop space: 2 sq ft per bird
- Run space: 5 sq ft per bird
Always give chickens more room if you can, since they like to run around and meet new people. Free ranging provides enrichment.
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Here are three different breeds of chicken, raised on the exact same diet:
The one on the left is a breed from 1957. The middle one is a 1978 breed. And the one on the right is a commercial 2005 breed called the Ross 308 broiler. They’re all the same age. And the modern breed is much, much, much larger.
In just 50 years or so, chickens have been bred to be much bigger. The above comes from a study done by researchers at the University of Alberta, Canada, who raised three breeds of chickens from different eras in the exact same way and measured how much they ate and how they grew. This allowed them to see the genetic differences between the breeds without influences from other factors like food or antibiotic use. They recently published their results in Poultry Science.
Chicken Coop Size Calculator – How big a chicken coop do you need?
FAQ
What’s the average size of a chicken?
The average size of a chicken varies significantly based on breed, age, and whether it’s raised for meat or eggs.
How big is a full chicken?
Whole chickens come in various sizes, generally ranging from 2. 5 to 8 pounds. Smaller chickens, like Cornish game hens, are typically under 2 pounds, while broiler/fryer chickens are between 2. 5 and 4. 5 pounds, and roasters are 5 pounds and over.
What size is a regular chicken?
The Domestic Chicken has a wingspan in the range of 23. 6”-35. 4” (60-90 cm) and total weight of 5. 7-9. 9 lb (2. 6-4. 5 kg). The body of the Domestic Chicken has an overall length between 15. 75”-23. 6” (40-60 cm), body width of 4. 5”-7. 1” (11. 5-18 cm), and standing height of roughly 9. 8”-14. 6” (25-37 cm).
How big are full grown chickens?
Large fowl chickens can range from 4 pounds for small hens to nearly 15 pounds for the largest roosters! Bantams vary in size, too. Oct 11, 2022.
Where can you find Big Chicken?
Big’s Chicken is a new business in Portland and Beaverton that was started by four chefs who love chicken very much. Big’s Chicken opened in April 2017. Chef Ben Bettinger, also the head chef at Laurelhurst Market, runs the kitchen.
What type of cuisine does Big Chicken serve?
Big Chicken is serving up some of the best chicken sandwiches with the BIGGEST flavor of all time. With taste at the forefront, Big Chicken delivers a menu that fuses home-cooked childhood favorites with bold new flavors. Come try our signature dish Lucille’s Mac ‘n’ Cheese, just the way mom made it – but with a crispy Cheez-It® crust!.
Does Big Chicken offer delivery services?
Yes, Big Chicken offers both delivery and takeout. What forms of payment are accepted? Big Chicken accepts credit cards. How is Big Chicken rated? Big Chicken has 4 stars.
What is the history of Big Chicken?
There is a dream team of partners behind Big Chicken. They are JRS Hospitality, a successful Las Vegas-based ownership group; Authentic Brands Group, a multinational, multi-billion-dollar brand development, marketing, and entertainment company; and Shaquille O’Neal, a basketball legend who is in the Hall of Fame.