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When Do Chickens Stop Growing? [And How Big Do They Get?]

A common question raised by chicken keepers is when they can expect their birds to stop growing. Besides, you need to prepare sufficient space for adult birds and get to work to ensure you have everything they need. But at what age can you expect a chick to reach their final adult size? I spent some time researching this poultry bird and will be sharing all that I found with you here today.

So, when do chickens stop growing? The average breed of chicken stops growing by 1 year of age. They generally reach their height by 7/8 months, but continue to fill out and gain weight for the next 4/5 months. Most of a chickens growth however, happens in the first 3/4 months of life.

It must be noted that there are hundreds of breeds of chicken in existence. Their color, comb type, amount of feathering, and size are all such characteristics that can differ, among others.

When it comes to keeping chickens however, there are general recommendations of what breeds to keep.

You’ll often see Plymouth Rocks, Orrington’s, Australorp’s, Cochin’s and Silkies make the list; all due to their friendly nature and suitability for a flock.

As such, we can soon begin to collect a sufficiently large, while not excessive, sample size and work out averages on how big they will likely get and when by.

So, let us know take a closer look at the development of a chicken, before we turn to their expected size.

We will also be looking at some of those other important questions such as how much room your chickens will need.

So, be sure to keep on reading to get all the information you need!

Development Of A Chicken

The development of a chicken begins the moment a rooster mates with a hen.

Let us now take a closer look at each phase so we can get an understanding of the growth of a chicken:

  • Egg Formation – A hen’s body begins forming an egg shortly after laying her previous egg. It takes around 26 hours for an egg to fully form [1].
  • Egg Incubation – It takes around 21 days for an chicken embryo to develop before it is able to hatch [2]. During this time, a hen will naturally incubate her eggs by sitting on them. Otherwise a humidified incubator will be required to fulfil the same role.
  • Hatching and Early Life – The first 1-4 weeks of life, chicks are considered ‘babies’. They require a complete starter-grower feed that must contain at least 18% protein. This will help support their growth and early development. Chicks at this age are vulnerable to illness and may require vaccination or medicated feed.
  • Teenage Phase – Between the weeks of 5-15, most of a chick/chickens growth will occur. It begins with the development of their plummage and primary feathers. It is at this age when differences between genders can be seen. Pullets (females) and Cockerel (males) are terms that can be now used.
  • Adult – From week 16 onwards, a chicken will generally be considered an adult. An adult chicken is one that is able to reproduce and lay their own eggs.

As you can see, within four months a small egg will develop into a reproducing chicken.

How Big Do Chickens Get?

How big a chicken will get will depend mostly on the breed. However, it is important to note that some breeds have a ‘bantam’ size – which is the word used for a smaller version.

Nevertheless, some chickens are naturally a lot larger than others.

It is therefore important to know of the different breeds and their expected sizes.

Besides, if you are looking to keep chickens, how big they get will have an impact on the size of the coop you get, along with what breeds are best for the space you have available.

Let us now take a closer look at some of the most commonly kept chicken breeds and their average and size categories:

Chicken BreedSizeSize Category
Silkies3-4 lbsSmall
Polish4-6 lbsSmall
Sussex4-6 lbsSmall
White Leghorn5-8 lbsMedium
Plymouth Rocks 6-8 lbsMedium
Rhode Island Reds6-8 lbsMedium
Easter Egger6-8 lbsMedium
Buff Orpington 7-8 lbsLarge
Wyandotte7-8 lbsLarge
Australorp7-10 lbsLarge
Brahma8-10 lbsLarge
Faverolle8-11 lbsLarge
Cochin9-11 lbsLarge
Jersey Giant10-13 lbsLarge

When it comes to selecting a chicken breed; size should not be the only factor that you take into account.

You also need to consider the individual personalities and temperaments of each breed, and more importantly, how they will all get along together if you are keeping multiple breeds together.

Flocks will naturally operate via a pecking order; a hierarchy of power where each chicken will know their place.

Some chickens are known to be more friendly and gentle, whereas others more loud and likely to ‘bully’ others.

Generally quieter chickens are less likely to become aggressive towards others.

At What Age Are Chickens Full Grown?

Chickens generally reach their full adult weight and size at around 1 year of age. Although this does vary somewhat by breed.

For instance, larger breeds tend to take somewhat longer to reach their full potential. The Jersey Giant, for instance, can take up to 16-18 months to fill out.

Nevertheless, chickens of all breeds go through the same development cycle.

A recently hatched chick and a mature chicken are fairly unrecognizable.

Beginning without feathers, lacking their combs and wattles, and sometimes not even being the same color as the breed standard.

However, chicks do develop quick.

Within 8 weeks they will have developed their feathers and will be taking on the characteristics and traits of their parents.

At around 12 weeks of age they will be about half the size of their final expected size.

From there, feathers, combs and wattles and slower weight gain will continue to develop over the upcoming months.

One important aspect of growth and one a keeper needs to be mindful of is feed.

Feed is essential to support healthy growth and to ensure a chicken reaches their full size potential.

It is equally important that a chicken consumes a feed that is designed with their weight and size in mind.

So, chickens, of any breed, should be given the following feed at these different stages:

  • Hatch day to 8 weeksStarter Feed (sometimes referred to as starter chick feed). This must contain at least 18-20% protein. No calcium supplementation is required at this age.
  • 8-18 Weeks Grower Feed – This must be at minimum 18% protein. If a chick started on 20% protein starter feed, they can be transitioned down to Grower. Otherwise, if the starter feed was already 18% no transition or change needs to be made. No calcium supplementation is required at this age.
  • 19 Weeks + – Layer Feed – contains 16% protein. Calcium supplementation via Oyster shells or crushed eggshells should be provided in a separate dish.

How Much Room Do Chickens Need?

How much room chickens need depends on four main factors: the breed of chicken you are looking to keep, whether or not they will allow to free roam, how long you intend to keep your birds in their coop and how many chickens do you intend to keep in your flock.

That being said; you do not need lots of land to be able to keep chickens.

The general recommendation is to allow a certain amount of square feet per bird.

The smaller the bird, the less square feet is to be afforded to them.

Here are some typical guidelines and recommendations for a coop:

  • Small Chicken Breeds – 2 square feet per chicken
  • Medium Sized Breeds – 3 square feet per chicken
  • Large Chicken Breeds – 4 square feet per chicken

Then there is the run, where birds can free roam and stretch their legs while still being protected from potential predators.

It is advised that each chicken has at least 15 square feet to roam.

If we consider that the average flock size for new keepers is 6, and the most common breed of chicken is medium in size, a keeper would need the following:

  • A coop that is 18 square feet,
  • A run that is 90 square feet.

So in total, this particular keeper would need 108 square feet to keep six chickens.

This equates to a yard/garden that is at minimum, 11 foot by 10 foot.

Let us now take a closer look at the living arrangements and their importance when keeping chickens:

In The Chicken Coop

The Chicken Coop is where your chickens will roost of an evening, or when the weather is particularly bad outside.

Its essentially the birds house.

This should not include the run or any other space that you intend to allow your birds to roam.

The Coop should have a floor covered in either sawdust or straw, and an area for your chickens to roost or perch.

The coop needs to be at least 2, 3 or 4 square feet per chicken, depending on the breed.

So for instance:

  • 4 Silkies (small sized chickens) would need a coop that is at least 8 square foot (4×2 square feet)
  • 6 White Leghorns (medium sized chickens) would need a coop that is at least 18 square foot. (6×3)
  • 8 Australorp’s (large sized chickens) would need a coop that is at least 32 square foot. (8×4).

You get the idea.

You may also be wondering if more space in the coop is better. It actually is not.

Too much space in the coop for your chickens and flock size is not ideal.

Its difficult for your birds to generate and retain enough heat to keep warm!

To Roam

Roaming, or being let out to wander, requires more space.

At a minimum, 15 square feet is advised per chicken.

So for a flock of 4 chickens you would need 60 square foot (4×15)

Thankfully, this is not much land.

In contrast to the coop, more land to roam is better and comes advised (if possible).

So, providing up to 30 square feet per chicken would be great, if you can.

Where and how your chickens roam is your choice, as the keeper.

You can create a run, or allow them to free roam on your property.

Both have their pros and cons, but the safety of your birds must be a priority.

Watching out for predators, like badgers, weasels, skunks, owls etc. depending on where you live is a must!

Nonetheless, the more space you can afford your chickens to roam the better. This helps to prevent diseases from passing between your flock, and keeps them away from tight spaces that can attract mold and bacteria.

Besides, it leads to a much happier flock.


Chickens are not the largest of birds, but they certainly grow up fast and require sufficient space to thrive.

If you are looking at keeping chickens, consider that there are actually quite a few differences between the breeds.

Not just in how they look, but in how big they will ultimately get and the personalities and temperaments they generally possess.

So, one of the best things you can do if you are serious about owning a flock, is to research into the various breeds and what is involved.

But ultimately, and irregardless of the breed you ultimately decide upon, these birds are great to keep.

Watching and helping them to grow and mature is one of the most rewarding things you can do.