When Do Jack Russell Terriers Stop Growing

All pet parents reading this article will surely agree when I say that raising Jack Russell from puppyhood into adulthood is very rewarding. This terrier is rectangular with a strong frame, despite having a compact build. You can find terriers with rough or smooth coats, with black or brown markings on their white bodies.

You must be aware of the immense energy and power this particular breed packs. Their historical breeding is the reason why these dogs demand extra physical and mental stimulation. Owing to the rigorous activities of Jack Russells, you will be wondering when your pet will stop growing.

If you raise them up well, you will have a devoted friend for life and a healthy pet dog. Let’s discuss their growth details below:

History of Jack Russells

Reverend John Russell wanted to create a breed that would serve as foxhounds. He wanted hunting companions that would chase foxes and be able to follow them right through their narrow underground passages.

As a result, he created the terrier breed that has the speed to chase larger hounds and tough enough to take down fierce, cunning opponents. Although Jack Russells originated in England, the breed, however, developed in Australia.

Growth of Jack Russells

In the case of Jack Russell terriers, you can expect them to reach their full size at the age of six to eight months. However, you can still expect your pet to continue to fill out until it is approximately twelve months of age.

This is the general expectation if your Jack is in perfect health and has sound genetics. The fact remains that your pet’s diet, health, and genetics determine its rate of growth. This is the reason why each Jack develops differently.

The growth depends largely upon the health and nourishment of your dog, while the genetics merely affect the height of your dog. Hence, if you want your pet Russell to reach their maximum growth and height, you must take care of them. Give them a proper diet, ample physical and mental stimulation. Foods that are nutrient-dense and plenty of exercise are sure to help your pet grow well.

Jack Russells- Height

Jack Russells have varying heights. Hence, there is no cause for concern if your particular Jack grows above or below the average height of the breed. Like I said, genetics, diet and health are major contributing factors so any differences in these will affect the proportions of each Russell individually.

Now, several more factors are responsible for the varying height and growth of Jack Russells. but it is always useful to have a rough idea of what size yours will grow to. To speculate how much your Jack Russell will grow to, it is a good idea to look at the size of their parents. When you observe the height, growth, and other stats of both the parents, you will have a fair idea of the full potential of yours.

A fully-grown Jack Russell will grow to an average height of ten or fifteen inches. The first twelve months of every Jack Russell’s life are the prime growing days. Your pet should grow to its maximum height within this time. In terms of weight, some Russells can continue filling out beyond this time.

Weight of Jack Russells

As is the case with the height, the weight of Jack Russells can vary per dog too. Hence, if you find your pet not growing to its average expected weight over a certain period, you need not feel overly concerned. It could be that your Jack is a small dog by nature, or it will possibly catch up with the required weight in time.

If you’re a first-time pet parent, you have every right to feel anxious about your pup’s proper height and weight. Therefore, here is a general estimate of the height and weight you can expect for your pet between the ages of three to twelve months.

When your Jack turns approximately three months old, you can expect it to weigh around 2.8 to 3.6 kg or 6.2 to 7.9 pounds. At the age of six months, you can expect it to weigh around 5.1 to 6.4 kg or 11.3 to 14.1 in pounds. At the age of twelve months, your Jack Russell must weigh at an average of 6.4 to 8.2 kg or 14.1 to 18.1 pounds.

Both a male and female Jack Russell can grow to the same height and size. It is also a fact that Jack Russells do most of their growing during the first twelve months of their lives. However, you must also note that the growth factors can vary. So it is possible that your pet may grow fully before this period too.

Hence, if you find the growth process of your pet stopping before time, there is absolutely nothing abnormal in that. Likewise, it is also possible for your Jack to keep filling in weight beyond twelve months. Therefore, it is also normal for a pet to be lightweight after its first birthday.

Factors that Affect the Growth of Jack Russells

As parents, we do feel anxious and rightfully so when we find our children under weight or short in stature. Similarly, being parents features the same concerns, anxieties and emotions for us. You may find that your puppy Russell did not grow to the height and weight you were expecting.

Generally, there is never any serious problem behind it because terriers are a fine breed with sound health. However, it can be helpful to find the reason behind their short stature so that you may lay your concerns to rest.

In order to help you figure out the causes of your dog’s short height, you must know the factors that could be potentially responsible for their short height.


Genetics do not impact the growth of your dog, but they do help you determine the size meant for your pet. Observing the parents helps estimate whether your dog will be a small one even when fully-grown or it will be among the larger category. If you find the parent’s small-sized, surely your Russell will turn out to be a small one too.

Now there is nothing within our power to change the height and size of our dog but what we can ensure is to give them a healthy diet with good exercise regularly. This will lay solid ground to help your dogs reach their maximum potential.


A poor diet can stunt anybody’s growth, so dogs are no exception. If by any chance, you fail to meet the nourishment and diet requirements of your Jack, they will surely not be able to grow well. You may not spot symptoms of malnourishment immediately, but with time, the effects of poor nutrition will show.

Your Russell needs a diet rich in minerals, vitamins, and amino acids, and insufficient quantities of these can create risks. May naïve or ignorant pet parents resort to supplements as a result, but I find it imperative to stress that supplements are not a solution.

The best way to ensure sound health and maximum growth of your pet is to give it healthy and nutrient-rich foods. Also, note that the early age of Jack Russells is the ideal day of development. You must feed them the best and healthiest diet possible during their young days. Also, give equal importance to physical and mental activities alongside, and you will see your dog grow beautifully.

Worm Infections

Worm infections in puppies can be detrimental to their growth: this condition may even stunt their growth altogether. Worms are the parasites in the bodies that make a puppy malnourished by stealing the nutrients and calories from its foods in the intestines.

In case of severe infestation, your puppy will not be able to grow at all until someone removes the worms completely. In such cases, it is best to meet a veterinarian posthaste to get rid of the worm infection.

Other Health Concerns

These might not be apparent at first, but your dog can have some underlying health concerns that might obstruct its growth. Several kinds of health issues that spoil the growth progress of your dog, but it can be difficult to figure out the exact cause.

A visit to your local vet is the best idea in case you develop doubts or find something suspicious in your dog’s health status. Immediate identification and treatment will be able to restore the normal growth progress of your dog.

Final Thoughts

Jack Russells take approximately twelve months to develop to their maximum, but some Russells may continue plumping up even beyond. We can also never call a Jack Russell completely developed until we see it reach its maximum mental maturity. With the help of the stats I have provided in this article and noting the behavioral transition of your dog, you shall be able to judge when your Jack has completed its full growth.