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How Big Do Rat Terriers Get? [Average Height, Weight and Size]

Rat Terriers are an interesting and relatively rare breed with a catchy name. They are not for everyone, especially because they are known for being so stubborn, just like most other terriers. But how big does this dog breed get? What can an owner expect in terms of their height, weight, and general size? Here is what you need to know.

So, how big do Rat Terriers get? Rat Terriers can range from 8-23″ (20-58.5 cm) in height and between 4-35 lbs (2-16 kg) in weight, on average, when fully grown. The large variance in size depends on whether they are a Toy, Miniature, or Standard (Decker Giant) Rat Terrier (smallest to largest). The parental dogs used in breeding define their final size.

Rat Terrier Size

Regardless of the type you opt for, Rat Terriers are not a big dogs by any stretch of the imagination.

Although they do a range, there can be some differences between the toy-largest version.

Their breed standard, therefore, does fall in the “small to medium” classification.

Let us now take a closer look at the average size of a Rat Terrier.

We’ll also be covering their growth rate and how long you can expect them to reach their adult size.

Equally, we will be looking at when they reach mental maturity and those factors that influence their final size.

So, be sure to keep reading until the end to ensure you get all the information that you need!

Average Rat Terrier Height, Weight And Size?

Rat Terriers do not come in only one size. Because of this, their height and weight vary greatly among the strains.

There are actually three different sizes in which you can find a Rat Terrier – medium, small, and toy.

This breed also goes by several different names – the American Rat Terrier, the Ratting Terrier, and the Decker Giant (which is often used in reference to the larger version).

Females are slightly smaller than males but the main difference between the two sexes is their personality.

  • Toy Rat Terriers typically reach a height of 8-12 inches (20-30 cm) and weigh between 4-6 pounds (2-3 kg).
  • A Miniature Rat Terrier has an average height of 8-14 inches (20-35.5 cm), and weighs in the range of 6-8 pounds (3-3.5 kg).
  • A Standard Rat Terrier will typically grow to a height of 14-23 inches (35.5-58.5 cm) and has a weight range that falls in between 12-35 pounds (5.5-16 kg)

As you can imagine, the size of a Rat Terrier is largely influenced by the parental breeds.

Therefore, if you are looking to get a Rat Terrier, you must have this in mind when visiting breeders. Look at the parental dogs, and discuss the expected sizes of their litters.

Nevertheless, the Rat Terrier was interestingly originally bred for farm work. As their name suggests, they were bred to hunt rodents (especially rats) both above and below ground.

So they needed to be of a sufficiently small size to undertake this task.

As such, they are athletic dogs; sturdy, compact, while being relatively quick and strong at the same time.

At What Age Are Rat Terriers Fully Grown?

Rat Terriers are considered to be one of the slower to mature breeds. In other words, it will take some time before they have finally stopped growing from puppyhood and reach their final adult size and weight.

Of course, it will also depend on whether you have a toy, miniature, or standard Rat Terrier.

The smaller they are, the sooner they will reach their full-size potential.

As an example, a standard size Rat Terrier puppy expected to be a medium-size dog needs 15 to 18 months to reach their full-sized frame. As for weight, your pup will be close to their second birthday before their weight stabilizes.

Equally, a toy Rat Terrier can reach their full size by 12 months; it’s not unheard of.

Any weight they add beyond this is unlikely to be muscle and is more likely to come in the form of fat (which must be managed and controlled. Often this is due to overfeeding or an inappropriate diet).

That being said puppies need to eat and to eat well to reach their full-size potential.

Generally, you can get a rough idea of how much your dog will weigh before they even reach adulthood.

To do this, take note of their weight at about 18 weeks and then double it. That should give you a ballpark figure.

Also, keep in mind that every dog is different and that yours may become fully grown either sooner or later than others from the same litter. There are multiple factors involved, but as long as you care for your dog right from a young age, they should reach their potential.

When Do Rat Terriers Mentally Mature?

Some owners would say that a Rat Terrier never matures mentally at all. Always remaining alert, energetic, goofy, and feisty.

While this may be true to some extent, we must not confuse the breed’s temperament and personality with immaturity.

Mental maturity is defined as the moment when your puppy actually begins to act and behave like an adult dog.

Maturity like this cannot be taught and it can often take a long time to fully develop.

You will notice little things happening slowly that should give you a hint that your pup is ready to grow up a little bit.

Puppies often get themselves into trouble when they cross lines that a more mature dog would not. Once they learn not to cross these lines, it is likely your puppy has become an adult and will calm down significantly.

Since there is no actual timetable for you to follow as to when this should happen, there are several signs that you can watch out for:

  • It is easier to calm and settle down your pup, and they are capable of self-soothing
  • Training is progressing because they are listening attentively and responding appropriately to the commands that they are given
  • Your pup recognizes social cues from both humans and other pets and responds to them in an appropriate manner.

It is rare to see a Rat Terrier that completely calms down even remotely before they become elderly.

In fact, they are one of the slowest breeds to mentally mature.

This is great news for families who have kids and who are very active. Rat Terriers are boundless balls of energy and they love to play with kids, especially the ones within their own home.

Your child will run out of energy long before your Rat Terrier will tire of the current game.

Another thing to note is that ale and female Rat Terriers mature mentally at different rates and with different personalities.

The males of the breed are often far more affectionate and outgoing than their female counterparts. Exuberant is a word used to lovingly describe them and they do a lot of jumping.

Because they also prefer to play games that are physically challenging, the males have an even more defined musculature than the female Rat Terriers.

The males are also known to be more emotionally stable than the females and they are far less likely to badly react to loss or stress. Males are very dominant and will push their boundaries even when they know that you are the alpha.

Female rat terriers are affectionate in their own way. While a male will jump up in your lap, the females take an approach that is more like a cat – they will wind themselves around your legs and rub.

The females of the breed have no dominance issues and are perfectly happy to let someone else lead.

This can be a critical factor when you have young children in the home, and you want the kids to be part of the initial obedience training.

Females also seem to pick up on new things quicker than males, meaning they may be just slightly more intelligent.

Unfortunately, they do not always use this intelligence for good. They can be downright manipulative in attempting to get what they want from you.

What Are The Factors That Influence Size And Growth Rate?

One of the biggest influences on the final size of your Rat Terrier will be its pedigree and genetics.

Originally, Rat Terriers were developed using a cross mixture of Manchester Terriers, Old English White Terriers, Beagles, Fox Terriers, Bull Terriers, and several others.

Since they were bred to hunt, farms all over the country had Rat Terriers to keep down the population of rats, mice, and other vermin. This is where the name Rat Terrier came from and they excelled at hunting because of their cunning and quick maneuvers.

Eventually, Italian Greyhounds and Whippets were added into the breeding line to make them even faster. Depending on which line of ancestry your pup has, they could be either small or medium.

While not always the rule, genetics plays a very important factor in size and growth. If you have a sire and a dam that both grow at a steady rate until they reach their predetermined size, the chances are that a litter of their pups will carry the same traits.

There are always exceptions of course, but in general, you can see what your pup will be like by looking at the parents.

The other factors that will influence their growth rate and eventual size are their daily food intake, the frequency of exercise, and the intensity of exercise that they get.

It can be difficult to know if you are giving your pup the proper amount of food to keep them at a healthy weight for their age and breed.

If you believe that your puppy may be a little bit on the light side, a good indicator is whether or not you can easily see their ribs.

If so, slowly add a little more food into every meal to get them back on track.

Alternatively, if you are unable to see or feel your dog’s ribs, they most likely are overweight. To correct this, you will want to give lesser food portions at mealtime and incorporate some extra exercise into their day.

When it comes to exercise, both the frequency and intensity of the exercise that they do can impact their growth and size.

For example, dogs who are constantly on the go may stay slim and not seem to be growing very much at all, but likely they have long, lean, and strong muscles.

Dogs that train hard or are working dogs may appear bulky when you look at them, but underneath that coat is solid muscle.


Rat Terriers are not the biggest of dogs, but the breed does come in a range of size depending on their genetics and parental lineage.

Either way, these are generally fast, strong and compact dogs; all of which were great traits and tendencies to have back in their working days.

As a family pet, it’s important to keep them somewhat retrained or even leashed when they are not in a fenced yard.

They are likely to take off like a shot if they see something worth chasing! They have a high prey drive as you can probably imagine.

However, as long as they get plenty of time outside to run and play, their smallish size means that they are well-suited even to apartment living.

Ultimately, If you’re looking for a loving companion with a fun personality, then this small to the medium dog could be a great choice for you.

Just be sure to ask questions with the breeder, do your research, and set your expectations. They make a great dog but they do require some work!

Related Questions

Are Rat Terriers A Good Family Dog?

Rat Terriers make great family dogs, they are perceptive of and attentive to their owners, have a high desire to please, love to be praised and also like to play. They are generally good with children along with other familiar dogs and cats.

However, this breed does have a somewhat stubborn streak and is vocal (liking to bark), so providing enough exercise and mental stimulation is required to keep them entertained and prevent destructive behaviors.

Equally early socialization and obedience training is considered a must for a better-rounded dog.

Are Rat Terriers Cuddly?

Rat terriers love attention, companionship, and being close to their owners. They love to cuddle and will often wrap their paws around their owners in order to get attention.

Often, Rat Terriers will follow their owners around the house; keen to be close and by their side at all times.

Want to learn more about the Rat Terrier breed? Then my following guides may be of interest:

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