How Big Do Bullmastiffs Get? Puppy Growth Chart and FAQ

Muscular full grown Bullmastiff

When it comes to your dog, some things are allowed to take you by surprise. But the potential size of your dog should not be one of those things. Before getting a dog, it should be safe to assume you already know if it’s a big breed or a small one. So, if you have decided on getting a Bullmastiff, you should know just how big your dog could get.

So how big do Bullmastiffs get? On average, a male Bullmastiff will weigh 110 – 130 pounds (50 – 59 kg) and 25 – 27 inches (63.5 – 78.6 cm) in height; females will be about 100 – 120 pounds (45.4 – 54.4 kg) heavy and 24 – 26 inches (61 – 66.04 cm) in height. These sizes are dependent on the health and condition in which Bullmastiffs are raised.

This article not only shed light on the potential size of your Bullmastiff but also reveals to you the factors affecting its growth and how you can make sure it remains within appropriate size. Keep reading to find out the average growth progression of your Bullmastiff puppy and everything in between.

How Big Do Bullmastiffs Get When Fully Grown?

Bullmastiffs can get very large when they attain physical maturity. Studies only show the average growth statistics of all Bullmastiffs, but there is a chance yours may be different.

What I mean is, your Bullmastiff might weigh more than the number you find here, and can also grow taller. In the same vein, it might be smaller than the average.

When they are fully grown, male Bullmastiffs can weigh between 110 – 130 pounds (50 – 59 kg) and will reach a height of 25 – 27 inches (63.5 – 78.6 cm). A female Bullmastiff ranges in weight from about 100 – 120 pounds (45.4 – 54.4 kg) and can get between 24 – 26 inches (61 – 66.04 cm) tall.

Do not expect your Bullmastiff to stop growing before it at least reaches the two-year mark.

As I have mentioned, the statistics documented here are just to give you a general idea of your Bullmastiff’s potential size. If it grows to become slightly bigger or smaller, you must not be alarmed. This is because a lot of factors come into play in deciding how big your Bullmastiff will get.

Your dog will grow to these sizes if its genes allow it. And that’s not all. You as the owner, have a part to play also. At full maturity, your Bullmastiff would have attained its true size if you were giving it the adequate nutrients it needed to grow.

Average Height and Weight by Age: What to Expect?

Bullmastiffs experience steady growth from the day they are born until they are fully grown. Even in their puppy stage, they can be as big as a full- grown Tibetan Terrier. At different stages of growth, Bullmastiffs need the right care to maintain steady growth.

It will help you to know how big your Bullmastiff will be at different stages. And so, I have created a growth chart to help you with that.

The table below shows the average height of Bullmastiffs from the second month until they’re fully grown:

AgeMale HeightFemale Height
2 months12 – 14 inches
(30.5 – 35.6 cm)
12 – 14 inches
(30.5 – 35.6 cm)
3 months18.5 – 20 inches
(47 – 50.8 cm)
18.5 – 20 inches
(47 – 50.8 cm)
4 months20 – 22 inches
(50.8 – 55.9 cm)
19 – 21 inches
(48.3 – 53.3 cm)
5 months21 – 23 inches
(53.3 – 58.4 cm)
20 – 22 inches
(50.8 – 55.9 cm)
6 months21.5 – 23.5 inches
(54.6 – 59.7 cm)
20.5 – 22.5 inches
(52.1 – 57.2 cm)
7 months21.5 – 23.5 inches
(54.6 – 59.7 cm)
20.5 – 22.5 inches
(52.1 – 57.2 cm)
8 months22 – 24 inches
(55.9 – 61 cm)
21 – 23 inches
(53.3 – 58.4 cm)
9 months22.5 – 24.5 inches
(57.2 – 62.2 cm)
21.5 – 23.5 inches
(54.6 – 59.7 cm)
10 months22.5 – 24.5 inches
(57.2 – 62.2 cm)
21.5 – 23.5 inches
(54.6 – 59.7 cm)
11 months23 – 25 inches
(58.4 – 63.5 cm)
22 – 24 inches
(55.9 – 61 cm)
12 months23.5 – 25.5 inches
(59.7 – 64.8 cm)
22.5 – 24.5 inches
(57.2 – 62.2 cm)
18 months24 – 26 inches
(61 – 66 cm)
23 – 25 inches
(58.4 – 63.5 cm)
Fully grown
(20 – 24 months)
25 – 27 inches
(63.5 – 68.6 cm)
24 – 26 inches
(61 – 66 cm)

The table below shows the average weight of Bullmastiffs from the first month until they’re fully grown:

AgeMale WeightFemale Weight
1 month9 – 12 pounds
(4.1 – 5.4 kg)
9 – 12 pounds
(4.1 – 5.4 kg)
2 months19 – 28 pounds
(8.6 – 12.7 kg)
17 – 25 pounds
(7.7 – 11.3 kg)
3 months37.6 – 42.9 pounds
(17.1 – 19.5 kg)
34.4 – 40 pounds
(15.6 – 18 kg)
4 months48 – 55 pounds
(21.8 – 24.9 kg)
44 – 52 pounds
(20 – 23.5 kg)
5 months58 – 66.3 pounds
(26.3 – 30.1 kg)
54 – 62.5 pounds
(24.5 – 28.3 kg)
6 months69.5 – 77.3 pounds
(31.52 – 35 kg)
63.8 – 74 pounds
(29 – 33.6 kg)
7 months74 – 85.5 pounds
(33.5 – 38.8 kg)
68 – 82 pounds
(30.8 – 37.2 kg)
8 months82 – 93.4 pounds
(37.2 – 42.4 kg)
75 – 87.8 pounds
(34 – 39.8 kg)
9 months89 – 98.6 pounds
(40.4 – 44.7 kg)
80.4 – 92 pounds
(36.5 – 41.7 kg)
10 months92.3 – 104.8 pounds
(41.9 – 47.5 kg)
84 – 99 pounds
(38.1 – 44.9 kg)
11 months97 – 110 pounds
(44 – 49.9 kg)
87.7 – 104 pounds
(39.5 – 47.2 kg)
12 months102 – 118 pounds
(46.3 – 53.5 kg)
93 – 110 pounds
(42.2 – 49.9 kg)
18 months105 – 121 pounds
(47.6 – 54.9 kg)
98 – 114 pounds
(44.5 – 51.7 kg)
Fully grown
(20 – 24 months)
110 – 130 pounds
(49.9 – 59 kg)
100 – 120 pounds
(45.4 – 54.4 kg)

As the table shows, female Bullmastiffs are smaller than males but not with a lot. The chart should give you a general idea of how your Bullmastiff will look like at the ages mentioned above.

But it is okay if your dog doesn’t meet up with or goes over the stat. As long as it is not overweight or underweight, then you shouldn’t worry too much.

Factors That Can Affect the Size of Bullmastiffs

Bullmastiffs are large dogs, and that is how nature intends it. So, by inference, it is unnatural if your Bullmastiff is not large. The size of your Bullmastiff is a huge part of its identity, but a lot can happen to alter the way it grows.

If your Bullmastiff is not as big as it should be or becomes way too big, something is off. Several factors can affect the size of Bullmastiffs, making them too small or overly large. Here are some of those factors.

  • Nutrition: The kind of food your Bullmastiff consumes will determine how well he will grow. From birth, Bullmastiff puppies feed on their mothers’ breasts, which contains all the necessary nutrients they need to grow. When they stop breastfeeding, you must ensure they do not stop receiving these nutrients. A well-balanced diet will ensure your Bullmastiff continues to grow at a steady pace until maturity.
  • Genetics: The genes a Bullmastiff carries is another factor that affects its size. Looking at the birth parents of a Bullmastiff will give you a look into its future. Hence, smaller Bullmastiff parents will most likely birth smaller Bullmastiff puppies. This is why it is advised that you should take a look at a puppy’s parent before choosing it. You will learn a lot by studying Bullmastiff’s parents.
  • Gender: For Bullmastiffs, males are generally bigger than females. So, if you get a female, do not expect her to outgrow a male (even though it could happen). Males will be about 10 pounds (4.5 kg) heavier, and around one inch (2.5 cm) taller.
  • Physical Activities: The level of physical activities a Bullmastiff engages in will determine its size. Say it gets all the appropriate nutrients in its meals, and it does not get exercise equivalent to that, surely it will get very big. Hence, Bullmastiffs need the right amount of exercise to ensure it maintains a healthy size.
  • Health: A healthy Bullmastiff will grow as it should. Diseases like hypothyroidism can cause a Bullmastiff to add too much weight, while cancer can cause it to lose too much. Also, endoparasites are a major cause of undergrowth in dogs. So, a Bullmastiff will grow in as much as it is in great health.

At What Age Do Bullmastiffs Stop Growing?

Larger dog breeds usually stop growing later than smaller dogs. There are a lot of controversies as to when Bullmastiffs stop growing. Because there has not been any scientific research on the subject, there are mostly speculations and personal experiences.

Each Bullmastiff is different and might get physically mature at different ages. Generally, a Bullmastiff will stop growing between the ranges of 18 to 20 months.

For some, it will stretch into their second birthday. At this stage, the Bullmastiff will no longer grow in height but will put on a few pounds more till its third birthday.

Will My Bullmastiff Still Grow After Being Neutered/Spayed?

There are some myths about how neutering/spaying dogs before puberty can cause stunted growth. In reality, performing these procedures actually causes an increase in height and can lead to a myriad of problems in the future. Of course, there are many upsides to spaying/neutering Bullmastiffs early, but the risks are much more.

The best time to spay your female Bullmastiff is to wait till after her first heat cycle. Males should be neutered until well after their second year. The reason for this is simple; Bullmastiffs are not like smaller breeds that become fully grown in 9 to 18 months.

They keep growing well into their second year (sometimes up to their third year). As they mature, the testes and ovaries produce hormones that determine their bones’ growth and shape.

Because Bullmastiffs still has some growing to do in their second year, neutering/spaying them earlier will cause problems. Early “fixing” will cause a delay in the closure of the growth plates, which will lead the dog to grow larger and lead to health issues in the long run.

Why Is My Bullmastiff Puppy Not Growing?

Stunted growth in puppies is very common. Bullmastiff puppies are no exception as they too can suddenly stop growing due to some factors. Stunted growth in Bullmastiff puppies means a sudden cessation of growth, where they become unable to increase in size.

The most common cause of stunted growth in Bullmastiff puppies (as well as other breeds) is endoparasitesOpens in a new tab.. Puppies easily get worms from their parents or their environment.

Worms like roundworms, tapeworms, and hookworm find their way into the intestines and wreak havoc. It is the infestation of these worms that cause a decrease in the growth rate of puppies.

However, endoparasites are treatable, and their damage is reversible. When growth begins to slow down, and you notice it, quickly visit your vet for the right medications to take care of the problem.

Another cause of stunted growth in Bullmastiff puppies is a liver shuntOpens in a new tab.. Although liver shunt is not very common in Bullmastiff puppies, it is surely existent. This health problem comes with a lot of symptoms, but one of the most noticeable is a slow growth rate in puppies.

Is Your Bullmastiff Overweight or Underweight?

It is not difficult to tell when your Bullmastiff is overweight or underweight. Knowing when your Bullmastiff’s weight has fluctuated into an unhealthy zone can be quite easy if you keep a constant record of its weight. But body mass is not always the only way to judge whether your dog has become overweight or underweight.

You can tell if your Bullmastiff is overweight or underweight by carefully studying them. All the tell signs are on its ribs, waist, shoulders, and even hips. If you look at your dog and see too much visible bone, it means he is underweight.

However, just the eyes cannot do enough justice. You will have to use your hands to feel your Bullmastiff’s body. If you cannot feel the bones in those joints, then your dog is overweight.

What to Do If Your Bullmastiff Is Overweight or Underweight?

The change in your dog’s weight could be as a result of health problems or its diet. The fact is, you cannot be entirely sure which of these is the cause, so the safest option is to seek advice from your vet.

If your Bullmastiff is getting overweight or underweight because of health issues, your vet is in the best position to help.

However, if your dog’s diet is the cause, it falls on you to make the necessary changes. Knowing when to give your dog more or fewer calories is key here.

Excess weight in your dog could be because it eats high-calorie food without getting enough exercise to burn the extra fat. And the opposite is true when your Bullmastiff is underweight.

How to Measure Your Bullmastiff’s Height?

Taking your Bullmastiff’s height measurement is not going to be as easy as checking its weight. To get the right height, you’ll need a bit more knowledge and the right information.

There are many reasons why you must know your Bullmastiff’s height and why the information must be correct. You’ll need the right height to be able to buy a suitable doggie door, for its medical records, to buy the right accessories, etc.

To get this process started, you’re going to need a carpenter’s level, a measuring tape, a pencil (as your marking tool), and finally, a door frame or wall.

A dog’s height is not measured from its paws to its head, because that would be wrong. The correct height is gotten when the measurement is taken from the paws up to the withers.

Step 1: Place Your Bullmastiff Straight Against a Wall

The first step to taking your Bullmastiff’s height measurement is getting it to stand straight against a wall. Note that you cannot force it to stand straight so you will have to come up with a creative way to get it.

I’ve found that the best way to do that is to seek the help of another person who would help you hold the dog or entice it with a treat.

Step 2: Feel for Its Withers

Bullmastiffs are not a very hairy breed, so finding their withers will not be a problem. The withers are the spot where the shoulders meet the neck, and this is the place you’ll need to place the carpenter’s level.

Although the Bullmastiff has short hair, you should still use your hands to feel for the withers to make sure you have the right spot.

Step 3: Place the Level Across the Withers of Your Bullmastiff

Take the carpenter’s level and place it across your Bullmastiff’s withers, ensuring the tip touches the wall. Remember, the level has to be straight for the measurement to be correct, so make sure your hands are steady.

Once you’ve done that, you can take the marker or pencil and indicate where the level touches the wall. That way, you have transferred your Bullmastiff’s height onto the wall.

Step 4: Take Your Measurements

At the last step, the hard work has been done, and all you need to do is get a figure. Take a measuring tape and measure the height from the ground up to the mark on the wall. The reading on the tape is the height of your Bullmastiff.

Size Information for Common Bullmastiff Mixed Breeds

Some amazing dogs have been produced from crossing or mixing Bullmastiffs. There are Bullbasset Mastiff, Clumberstiff, Bully Bordeaux, Golden Bullmastiff Retriever, Bullmasador, Bull Mastweiler, and so forth. So, if you want the great traits of the Bullmastiff mixed with some of these breeds, you can have your pick.

Pit Bullmastiff

First on my list is the Pit Bullmastiff, a hybrid gotten from the combination of the Bullmastiff and the American Pitbull Terrier. Separately, the Pitbull and the Bullmastiff are quite large; hence their mix is also large.

Males can weigh 120 – 150 pounds (54.4 – 68 kg) and be as tall as 27 – 29 inches (68.7 – 73.7 cm). On the other hand, females can be anywhere between 100 – 130 pounds (45.4 – 59 kg) heavy and 25 – 27 inches (63.5 – 68.6 cm) in height.

Clumberstiff

The Clumberstiff is a mix of the Bullmastiff and the Clumberstiff Spaniel. This combination is a pretty nice one, and the Clumberstiff inherited more of the Bullmastiff’s size.

Male Clumberstiffs can be between 22 – 24 inches (55.9 – 61 cm) tall and 90 – 110 pounds (40.8 – 49.9 kg) heavy. Females are slightly smaller, weighing about 80 – 100 pounds (36.3 – 44.4 kg) and reaching a height of 21 – 23 inches (53.3 – 58.4 cm).

Bull Daniff

Mixing the Bullmastiff and the Great Dane gives us the Bull Daniff. These are a very large breed as both parents are large.

Male Bull Daniffs, on average, can grow as big as 160 – 200 pounds (72.6 – 90.7 kg) and be as tall as 33 – 34 inches (83.8 – 86.4 cm). Females are not far behind, weighing about 115 – 150 pounds (52 – 2 – 68 kg) and reaching a height of 32 – 33 inches (81.3 – 83.8 cm).

Golden Bullmastiff Retriever

The Golden Retriever’s genes slightly reduce the size of the Bullmastiff and soften its appearance. The mix between these two is called the Golden Bullmastiff Retriever. The size difference between both males and females is not extremely large, but it is present.

Males can weigh 95 – 110 pounds (43.1 – 49.9 kg) and have a height of 25 – 27 inches (63.5 – 68.6 cm). On the other hand, females weigh between 85 – 100 pounds (38.6 – 45.4 kg) and can get as tall as 23 – 25 inches (58.4 – 63.5 cm).

Doubull-Mastiff

Doubull-Mastiff is a mix between the English Mastiff and the Bullmastiff. Considering the sheer size of its parents, the Doubull-Mastiff is a giant.

The size charts for male and female Doubull-Mastiff show that there are no differences in their sizes. Both males and females weigh between 130 – 200 pounds (59.90.7 kg) and can be as tall as 27 – 36 inches (68.6 – 91.4 cm).

Staffy Bull Bullmastiff

The Staffy Bull Bullmastiff is one of those dog breeds that can either be a giant, or medium-sized. Staffy Bull Bullmastiffs are a cross between Bullmastiffs and Staffordshire Bull Terriers. With this breed, your dog’s size will come as a surprise to you because you will either get a large dog or a medium one.

Males weigh between 38 – 130 pounds (17.2 – 59 kg) with a height of 14 – 27 inches (35.6 – 68.5 cm), while females weigh around 34 – 120 pounds (15.4 – 54.4 kg) and have a height of 14 – 26 inches (35.6 – 66 cm).

My Final Thoughts

The size of a Bullmastiff can become a big problem for those who do not know how to handle big dogs. This is a major reason they are not recommended for novice owners. Regardless of the extraordinary personality of Bullmastiffs, they will still be a challenge for first-time dog parents.

For everything you would do for a small dog, you would have to double for the Bullmastiff. This is why it is important to know how big these dogs can get when fully grown. You will need to know the kind of accessories, food, and care this dog needs and that knowledge will depend on knowing their size.

John Carter

My name is John Carter and I absolutely love pets, especially dogs. I've got a Bachelor of Science degree in Animal Behaviour and Welfare and have several years’ experience working in animal shelters and rescues. My passion for animals started at a very young age as I grow up on a farm with several horses, cows, cats, chickens, and dogs on our property.

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