How Big Do Mastiffs Get? Puppy Growth Chart and FAQ

Full grown English Mastiff lying on the grass

One crucial factor to consider before getting a dog (especially a big one), is to consider how big they could potentially grow. This is vital because you’ll need to know whether you will have enough room for the dog in your apartment or on your couch.

So, considering getting the good-natured Mastiff? Is your furniture strong enough to hold up these black giants?

How big does a full-grown Mastiff get? The size of the Mastiff is what you’d call sexually dimorphic, which refers to a difference between the weight and height of males and females. Males will be 27 – 30 inches (68.6 – 76.2 cm) in height and 160 – 230 pounds (72.6 – 104.3 kg) in weight, while the females will be around 25 – 27.5 inches (63.5 – 69.9 cm) in height and 120 – 170 pounds (54.4 – 77.1 kg) in weight.

The purpose of this article is to give you an in-depth idea of what to expect in respect to your Mastiff’s size, the various factors that affect how big they could grow, and other vital size-related details. To find all your answers, let’s go into the article proper.

How Big Do Mastiffs Get When Fully Grown?

It will be impossible to determine the exact size a specific Mastiff dog will get to when he’s fully grown. But an average range can be determined of all Mastiff dogs.

The general information, as given by the American Kennel Club, shows that male Mastiffs grow to become as massive as 230 pounds (104.3 kg), while females can weigh as much as 170 pounds (77.1 kg). Males can get as tall as 30 inches and more (76.2 cm), while females grow up to 27.5 inches (69.9 cm).

These statistics were given due to the observations that were made on this breed. And these numbers given were meant to give a potential Mastiff parent a general idea of what to expect of their dog.

However, with more research, we found that some Mastiffs have exceeded the weight range of this breed. Not long ago, I met a Mastiff parent whose male weighed 256 pounds (116.1 kg), which was more than the weight stipulated by the AKC.

The weight of the heaviest Mastiff ever recorded was 343 pounds (155.6 kg) in 1989. Aicama Zorba, which was the name of the dog, was seven years old, and he was from England. This only goes to show that there is a possibility that your Mastiff may exceed the weight range given by AKC. So maybe you should just keep that at the back of your mind.

Average Height and Weight by Age: What to Expect?

They were once tiny puppies like most other breeds. They were cute, tiny, and as cuddly as others before growing up to be the Giants we know them to be. However, even as puppies, it is relatively easy to tell that Mastiffs will grow up to be very big dogs by looking at their paws’ size.

Let us look at the average weight and height of Mastiffs from when they are one month old until they stop growing.

The table below shows the average height of Mastiffs from the second month until they’re fully grown for both genders:

AgeMale HeightFemale Height
2 months14 – 15 inches
(35.6 – 38.1 cm)
13 – 14.5 inches
(33 – 36.8 cm)
3 months20 – 22 inches
(50.8 – 55.9 cm)
19 – 21 inches
(48.2 – 53.3 cm)  
4 months21.5 – 23 inches
(54.6 – 58.4 cm)
20 – 22 inches
(50.8 – 55.9cm)
5 months22 – 23.5 inches
(55.9 – 597 cm)
20.5 – 23 inches
(52.1 – 58.4 cm)
6 months22.5 – 24 inches
(57.2 – 61 cm)
21 – 23.5 inches
(53.3 – 59.7 cm)
7 months22.5 – 24 inches
(57.2 – 61 cm)
21 – 23.5 inches
(53.3 – 59.7 cm)
8 months23 – 24.5 inches
(58.4 – 62.3)
21.5 – 24 inches
(54.6 – 61 cm)
9 months23.5 – 25 inches
(59.7 – 63.5 cm)
22 – 24.5 inches
(55.9 – 62.2 cm)
10 months24 – 25.5 inches
(61 – 64.8 cm)
22.5 – 25 inches
(57.2 – 63.5 cm)
11 months24.5 – 26 inches
(62.2 – 66 cm)
23 – 25.5 inches
(58.4 – 64.8 cm)
12 months25 – 26.6 inches
(63.5 – 67.6 cm)
23 – 26 inches
(58.4 – 66 cm)
13 months25.5 – 27 inches
(64.8 – 68.6 cm)
23.5 – 26.5 inches
(59.7 – 67.3 cm)
14 months25.5 – 27 inches
(64.8 – 68.6 cm)
23.5 – 26.5 inches
(59.7 – 67.3 cm)
18 months26 – 29 inches
(66 – 73.7 cm)
24 – 27 inches
(61 – 68.6 cm)
Fully grown
(24 months)
27 – 30 inches
(68.6 – 76.2 cm)
25 – 27.5 inches
(63.5 – 69.9 cm)

The table below shows the average weight of Mastiffs from the first month until they’re fully grown for both genders:

AgeMale WeightFemale Weight
1 month10 – 15 pounds
(4.5 – 6.8 kg)
8 – 13 pounds
(3.6 – 5.9 kg)
2 months24 – 30 pounds
(10.88 – 13.6 kg)
20 – 30 pounds
(9 – 13.6 kg)
3 months30 – 47 pounds
(13.6 – 21.3 kg)
35 – 47 pounds
(15.9 – 21.3 kg)
4 months35 – 60 pounds
(15.9 – 27.2 kg)
52 – 65 pounds
(23.6 – 29.5 kg)
5 months50 – 82 pounds
(22.7 – 37.2 kg)
60 – 82 pounds
(27.2 – 37.2 kg)
6 months70 – 110 pounds
(31.8 – 49.9 kg)
70 – 90 pounds
(31.8 – 40.8 kg)
7 months85 – 132 pounds
(38.6 – 59.9 kg)
80 – 105 pounds
(36.3 – 47.6 kg)
8 months100 – 152 pounds
(45.4 – 68.9 kg)
90 – 115 pounds
(40.8 – 52.2 kg)
9 months108 – 165 pounds
(49 – 74.8 kg)
95 – 125 pounds
(43.1 – 56.7 kg)
10 months115 – 178 pounds
(52.2 – 80.7 kg)
100 – 130 pounds
(45.4 – 59 kg)
11 months120 – 185 pounds
(54.4 – 84 kg)
105 – 140 pounds
(47.6 – 63.5 kg)
12 months125 – 190 pounds
(56.7 – 86.2 kg)
110 – 150 pounds
(50 – 68 kg)
13 months130 – 198 pounds
(59 – 90 kg
113 – 155 pounds
(51.3 – 70.3 kg)
14 months132 – 199 pounds
(59.9 – 90.3 kg)
115 – 157 pounds
(52.2 – 71.2 kg)
18 months145 – 210 pounds
(65.8 – 95.3 kg)
119 – 160 pounds
(54 – 72.6 kg)
Fully grown
(24 months)
160 – 230 pounds
(72.6 – 104.3 kg)
120 – 170 pounds
(54.4 – 77.1 kg)

The table above represents the average height and weight of Mastiffs (male and female) at different stages of life. While this will not give you a specific size, it is meant to provide you with a general idea, so you know what to expect. And knowing that helps you make the necessary preparations.

Females usually aren’t as big as males. The size difference is actually enormous, as you can see from the tables. You will notice that your Mastiff’s growth progresses at a steady rate up until its eight months when growth begins to slow.

This shows that your dog will do most of its growth before its eighth month. The same is true for both males and females, and both will be fully grown at around the age of two.

Factors That Can Affect the Size of Mastiffs

Mastiffs are, by nature, a huge dog breed. It is no wonder some refer to them as giants. But even with the average weight and height range that Mastiffs are said to reach, you could find that yours is either not meeting up or has gone over. The question you will want to ask yourself when such occurs is if more/less weight is normal.

Just like humans, Mastiffs can become overweight or underweight when certain factors come into play.

Below are some of the factors that positively or negatively affect the size of male and female Mastiffs:

  • Feeding: Food is one of the most common factors that affect Mastiffs’ size. A Mastiff that eats regularly maintains a healthy weight, but one that doesn’t eat will become malnourished and lose weight. Excessive eating (without regular exercise) will cause your dog to become overweight. This is a good reason why your male Mastiff could go well above 250 pounds (113.4 kg). In the same vein, when Mastiffs eats an inadequate amount of food, they risk becoming underweight.
  • Wrong diet: Aside from eating adequately, your Mastiff has to eat the right food. Mastiffs, like every other dog, need different types of food that provide the necessary nutrients needed for their healthy growth. The right combination of fats, carbohydrates, proteins, etc., is necessary for Mastiffs to get the required energy but will prevent them from gaining too much weight. At different stages of their lives, they need different kinds of diets. So, feeding puppy food to a senior Mastiff is sure to cause overweight. Also, high-quality food should always be chosen.
  • Exercise: Mastiffs have a very high potential to gain weight; hence they need lots of exercise. A good way for your Mastiff to grow bigger is excess (or even adequate) eating without proper and adequate exercise. Puppies are given food with higher calories because they are more active and are sure to burn excess fat. But if a high-calorie diet is given to a senior Mastiff who hardly goes through his daily exercise, he is sure to get bigger.
  • Medication: Prescription drugs have been known to alter the weight of dogs a lot of the time. This occurs mostly when the dog has been on the same meds for a long period of time. Whether it is a loss of weight or weight gain, you can do something to change it. The solution to this problem is asking your vet for a change of prescription. Surely, there are different approaches to treating some medical issues. So, if current medications are causing a change in weight, another therapy method can be looked into.
  • Health Defects: Sickness and diseases are a major factor affecting the size of Mastiffs. A healthy 150 pounds (68.03 kg) female Mastiff can lose weight when she comes down with certain diseases, such as cancer. In the same way, she can add a lot of pounds when she gets a disease like hypothyroidism. So, if you notice a drastic increase or decrease in the size of your Mastiff, for safety sake, take them to a vet for checkups.
  • Parental Gene: There are many reasons why potential dog parents are told to visit kennels before purchasing or adopting a dog. The reason being that you can learn a lot about your puppy just by looking at his parents. The same applies to size. To get a general idea of how big your female Mastiff will become, look at her mother. And to get an idea of how big your male Mastiff will be, check his father. You can hardly go wrong with this method. Mastiffs will usually grow to look like their parents. This is because genes are passed from parents to children. So, the same way you can tell that a dog will be healthy just by studying his heritage is the same way you can guess how big he will get.
  • Gender: The gender of a Mastiff determines his size. Males are generally 40 – 70 pounds (18.1 – 31.8 kg) heavier than females, and 2 – 3 inches (5.1 – 7.2 cm) taller. So logically, you cannot expect a female to grow bigger than males, especially if they are from the same litter.

At What Age Do Mastiffs Stop Growing?

There has not been any scientific research done to accurately determine the exact time Mastiffs stop growing. But from my own experience and that of other Mastiff owners I have posed this question to, the answer is fairly dynamic.

The most important take away is that each Mastiff is unique. So, if your dog doesn’t meet the average expectation, you shouldn’t feel too concerned.

Unlike some other canines, it takes Mastiffs about two years on average to stop growing. At the age of two, Mastiffs would be quite close to (if not already at) their adult height.

Some Mastiff parents would tell you their dog kept growing even after two years old. But what happens is that, at that age, they are mostly filling out and growing into their bodies.

As a result of this, a Mastiff is not considered fully grown until he is up to the age of 3. A fun fact is that, not only do Mastiffs take longer to grow physically, they also take longer to attain full mental maturity. That means Mastiffs have a longer “puppy age” than most other dog breeds.

Will My Mastiff Still Grow After Being Neutered/Spayed?

The simple answer to this question is yes. However, there is a “but.” Every dog breed has a recommended time when they should be neutered/spayed. The time for smaller dog breed differs greatly with that of larger breeds.

Most small dog breeds are neutered/spayed about when they turn six months, but the same cannot and should not be done with Mastiffs.

Neutering/spaying a Mastiff below one year can have a lot of effects, including growth patterns. Neutering a male before his growth plate closes can cause him to grow taller than he should. This may sound good, but seeing as the Mastiff is a large dog, it will cause a huge joint problem in the near future.

Male Mastiffs should be neutered between the ages of 18 to 24 months. They have almost grown into full size at that time, and neutering will not stop them from rounding out nicely. On the other hand, females should be spayed between the ages of 14 to 18 months to avoid the same problems.

So, to put it simply, neutering/spaying your Mastiff will not adversely affect their growth if the procedure is done at the right age bracket.

Why Is My Mastiff Puppy Not Growing?

If your Mastiff is not growing as it should, or not growing at all, then they are stunted. That means something is stopping them from growing at a natural rate. There exists a number of things that causes stunted growth in Mastiff puppies. Below are some of them.

Worms

One of the most common causes of stunted growth in puppies is hookworm or roundworm infection. Puppies easily contract intestinal worms, either from their surroundings or from their parents.

Heavy infestation of worms in a puppy can slow down their growth. When such infestation occurs, other symptoms aside from stunted growth also become visible. For instance, the puppy hair coat looks poor, has a big pot belly, will look very thin, and will experience diarrhea.

The good news about this is that the puppy can go back to normal and resume growth if and after receiving treatment.

Liver Shunt

This is a fairly uncommon cause of stunted growth in Mastiff puppies. A liver shunt is a condition that occurs when blood is carried around the liver by blood vessels instead of simply carrying it through the liver.

As a result, blood has circulated the body before being filtered by the liver (the liver cleanses the blood and rids it of bacteria and toxins). Unfiltered blood in the body can cause a lot of major problems for puppies, and one is stunted growth.

Some people tend to attribute stunted growth to a lack of proper nutrition. So, when they notice their puppy isn’t growing, they try to feed it more or use more supplements. This could worsen the problem.

So, the best thing to do when you notice abnormal growth in your puppy is to visit a vet. Get your Mastiff properly checked so that you can provide the right help.

Is Your Mastiff Overweight or Underweight?

To give your Mastiff a good, active, and healthy life, you must help them maintain a healthy weight. This will boil down to two major factors; their food (calorie) intake and exercise intensity.

There are other reasons why your dog could become underweight or overweight apart from feeding and exercise, such as diseases and medication.

Certain health issues can make your dog go way below normal weight (like parasites, diabetes, teeth conditions), and other issues exist that could make your dog gain too much weight (hypothyroidism).

Your dog’s health rests on knowing the changes in their weight and taking immediate action to make it right.

How to Tell If Your Mastiff Is Overweight or Underweight?

The best way to tell when your dog has either become overweight or underweight is by taking him/her to a pet nutritionist or a vet. They will give you the exact percentage of your dog’s body fat. However, if that seems too much stress for you, then there are other ways to find that out yourself at home.

One way to determine whether your Mastiff is overweight or underweight is to analyze their profile. Usually, dogs’ abdomen is higher up than their ribcage. A side view of your dog will show an incline from the rib area to their waist.

If the incline is too steep, then your dog is underweight. But if the incline is shallow or not present at all, then your dog is overweight. The best way to inspect the profile of your Mastiff is to lower yourself to the same level so you can view his body from side to side.

Another way I perform this test is to exam the dog’s ribs. All you have to do is to place both your thumbs on his spine and spread your palms out over his ribcage.

If all you can feel is his ribs, then your dog is underweight. But if you can’t feel his ribs at all, then he is overweight. Remember to do this with your hand and not your eyes, as his coat can easily cover his ribcage.

What to Do If Your Mastiff Is Overweight or Underweight?

If your dog is getting overweight or underweight, the best course of action will be to take them to a vet to determine the actual cause. If the reason(s) is medical related, then you need the help of vet or pet nutritionist to advise you and possibly provide a solution. But if the reason is due to feeding and exercising, then you can easily remedy that yourself.

If your dog is eating food with high calories, then you need to keep him active in other to burn excess fat. In colder weather where exercising outdoors is not an option, you can reduce his calorie intake to make up for the lack of exercise. You just need to know how to balance it out to make sure your dog stays within average weight.

How to Measure Your Mastiff’s Height?

Keeping track of your dog’s height is crucial if you wish to know/monitor their growth. Taking your Mastiff’s measurement is pretty easy, and you do not require a lot of tools to get it done.

Measurement is done from the floor up to the dog’s withers (the highest point of the shoulder blade), and you can always get the correct measurement. Below is a step by step process on how to measure your Mastiff’s height.

Step 1: Stand Your Mastiff Against the Wall

To get the right measurement, your dog must be standing either against a wall or a door frame. Make sure he is standing straight, stance squared, and feet spread apart at shoulder width.

Step 2: Identify Your Mastiff’s Withers

Next, you should feel for your Mastiff’s withers with your hand. You will find it situated at the base of his neck, and it will feel pointy.

Step 3: Place a Long Level Across Your Mastiff’s Shoulders

Get a long level and place it across your Mastiff’s withers so that the end touches the wall. Make sure the level is straight, then mark the spot on the wall where it touches. That way, you have marked your dog’s height on the wall.

Step 4: Measure From the Ground to the Mark on the Wall

Move the dog from the wall so that you can measure from the ground to the mark on the wall. The number you get is the height of your Mastiff.

Size Information for Common Mastiff Mixed Breeds

Mastiffs can be crossed with a lot of other dog breeds to produce some fantastic pets. Some of the breeds known to have been mixed with the Mastiff are; Labradors (Mastador), Pitbull (Mastibull), Rottweiler (Mastweiler), Saint Bernard (Saint Mastiff), etc.

Mastador

Mastadors are known to grow very big. Almost as big as the Mastiff. On average, Mastadors weigh between 100 – 200 pounds (45.4 – 90.7 kg) and stand between 28 – 36 inches (71.1 – 91.4 cm) tall. Females tend to be smaller than males.

Mastibull

Pitbulls are not nearly as big as Mastiffs, so the product of their mix (Mastibull) is not giant. They weigh between 65 – 160 pounds (29.5 – 72.6kg) and will reach a height between 21 – 27 inches (21.3 – 68.6 cm).

Mastweiler

The Mastweiler, which is a mix between the Mastiff and Rottweiler, is one of the best guard dogs from all Mastiff mixed. They will measure between 25 – 30 inches (63.5 – 76.2 cm) in height and will get as big as 90 – 190 pounds (40.8 – 86.2 kg).

My Final Thoughts

Experts will usually advise that you think thoroughly before getting a giant dog. This is because the responsibility attached to raising a big dog is incomparable to that of raising a smaller dog. As a result, a lot of thought should be put into such a decision.

The Mastiff is one of those breeds you have to think about before adopting or buying. While they are enormous, they need a strong human parent. But through and through, they are big cuddly babies in a large body.

One of the ways you can take care of your Mastiff is by regulating his weight. Keep him from getting overweight or underweight, and provide all the necessities he needs to stay healthy and happy.

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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