American Mastiff Growth Chart (Weight Chart & Size Chart)

The enormous Mastiff is a member of a canine group that predates civilization. The Mastiff is a big, heavy-boned dog with incredible tenacity and strength. He is placid and dignified, but also a fearsome protector of the people he loves. 

A first encounter with these black-masked giants can disconcert for the inexperienced. Males stand at least 30 inches tall and can easily outweigh several full-grown men. The rectangular body is muscular and deep, with a short double coat of fawn, apricot, or brindle stripes. The head is large and substantial, and a furrowed brow emphasizes an attentive, friendly face. 

Mastiffs make excellent friends and guardians because they respond well to gentle training. Mastiffs are fiercely loyal to their families, and their natural suspicion of strangers causes early socialization and training. Mastiffs make wonderful pets, but getting a robust giant-breed dog is a serious commitment.

If you are interested in American Mastiff growth chart, read the entire article!

American Mastiff Growth Chart
American Mastiff Growth Chart

When Do American Mastiffs Stop Growing?

Around one year of age, most dogs of this breed will reach their adult height. American Mastiff puppies require two to three years to fully develop and mature.

Compared to small to medium canines, enormous dog breeds might take years to mature. Use our American Mastiff weight chart above to keep track of your pup's growth stage and to ensure they remain within a reasonable range.

American Mastiff Size, Weight, Height Chart

Here is the size chart of an American Mastiff:

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)
American Mastiff Size Chart

What is the Standard American Mastiff Size

The American Mastiff is a dog that can only be characterized as a colossus. This colossal canine may weigh nearly 200 pounds and reach a height of 36 inches.

American Mastiff Growth Chart – What To Expect

What to expect with the growth of an American Mastiff
What to expect with the growth of an American Mastiff

American Mastiff Weight 3-12 weeks

Your puppy spends the first eight weeks of his/her life learning how to be a DOG. By 8 weeks, the pups had grown from blind, deaf pups weighing 1–12 pounds at birth to 16–20 pounds of running, eating, and playing with bundles of fur.

This is also the period of attraction — the period of attraction lasts from 6-8 weeks to approximately 5-6 months. The pup's natural impulses during this time are to FOLLOW and to be obedient to the family's leaders (human and 4 legged.) Take advantage of this. Your puppy will want to keep a close eye on you. This is the time to practice on leash and recall training.

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It will experience a sensitive/fear episode during this time. This often lasts until the third month of life. Noises, the presence of unusual things (a new garbage can, an Amazon box), and strange dogs can cause your pet to flee for protection or hide behind you. This is a natural period, and the best strategy is to remain cool, relaxed, and confident. Your puppy will pick up on your cues.

American Mastiff Weight 4-6months

Male American Mastiffs weigh between 60 and 110 pounds at six months of age. In comparison, the average female American Mastiff puppy weighs between 60 and 90 pounds.

According to the American Humane Society, one in every three canines becomes lost over their lifespan. 

American Mastiff Weight  7-9 months

Your AM puppy has grown into a BIG puppy. That same beautiful puppy that used to follow you everywhere and was always eager to run when he heard his name seemed to have gone deaf. Your puppy is maturing into an adolescent! Hold on, things are about to get interesting. You can expect your American Mastiff to grow 85 to 132 pounds and 22.5 to 25 inches long!

American Mastiff Weight  10-12 months

Your AM is about to reach full-fledged adolescence, and teens can be difficult to deal with at times. During this critical period, your pup will discover his bark. You can expect your American Mastiff to grow 115 to 185 pounds and 24 to 26 inches long!

Visitors, passing dogs, and new things may all be greeted with an imposing bark. Your puppy may regress in housebreaking — typically not through accidents, but through chewing on items that are off bounds. This phase is quite damaging and may involve shoes, remote controls, door frames, and walls. Your puppy may become extra protective during this time. During this time period, protective barking and lunging at passersby may occur during walks.

What is the Full Grown American Mastiff Weight?

A mature male English Mastiff weighs between 160 and 230 pounds, while a mature female weighs between 120 and 170 pounds.

What Is An American Mastiff's Neck Size?

American Mastiffs have the broadest necks of any mastiff breed, measuring between 28 and 38 inches in circumference. This makes them particularly challenging to fit, as many big and extra-large collars only reach a maximum length of 26″.

How Big Do American Mastiffs Get?

The American Kennel Club recommends that a fully mature American Mastiff male stand at least 30 inches (2 ft. 6 in) at the shoulder. At maturity, an American Mastiff female should stand at least 27.5 inches (2 ft. 4 in.) tall at the shoulders.

American Mastiffs, male and female, should be symmetrical, powerful, and rectangular in shape.

When do American Mastiffs stop Growing?

The mastiff is a large dog when fully grown. Male mastiffs must be at least 30 inches tall at the shoulder, while female mastiffs must be at least 27.5 inches tall at the shoulder. Expect your mastiff to weigh in at around 200 pounds. However, this colossal breed matures more slowly than ordinary canines. They are not regarded as fully mature until they reach the age of three.

Factors That Affect American Mastiff Puppy Growth 


Many reasons exist for potential dog parents to tour kennels prior to gaining or adopting a dog. The reason for this is that you may learn a great deal about your puppy simply by observing his parents. The same is true for size. Consider the size of your female Mastiff's mother to get an estimate of how large she will grow.

To determine the size of your male Mastiff, consult his father. This strategy is almost impossible to go wrong with. Mastiffs typically develop to resemble their parents. 

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This is because genes are passed on from parents to offspring. Thus, just as you can predict whether a dog will be healthy just by researching his ancestors, you can also predict how big he will become.

Diet & Nutrition

Diet of an American Mastiff
Diet of an American Mastiff

Food is one of the most common elements affecting the size of Mastiffs. A Mastiff that consumes food consistently keeps a healthy weight, whereas one that does not consume food will become malnourished and lose weight. Excessive eating (in the absence of consistent activity) will cause your dog to become overweight. This is a solid reason your male Mastiff may weigh far over 250 pounds (113.4 kg). Similarly, when Mastiffs consume an insufficient amount of food, they risk getting overweight.

Apart from eating enough, your Mastiff must eat the proper diet. Mastiffs, like all dogs, require a variety of various types of food to ensure proper growth. The proper combination of fats, carbohydrates, and proteins, among others, is vital for Mastiffs to get energy while avoiding excessive weight growth. They require a variety of diets at various phases of their life. Thus, offering puppy food to a senior Mastiff will almost certainly result in obesity. Only high-quality meals should be picked.

Physical Activity & Health

Mastiffs have a great propensity for weight gain; as a result, they require plenty of activity. Excess (or even adequate) feeding without correct and adequate activity is an excellent way for your Mastiff to develop in size.

Puppies are fed calorie-dense food since they are more active and are certain to burn off excess fat. However, if a senior Mastiff who barely exercises every day is fed a high-calorie diet, he will inevitably gain weight.

Will My Mastiff Continue to Grow After Being Spayed/Neutered?

Yes, this is the straightforward answer to this question. There is, however, a “but.” Each dog breed has a recommended age for neutering/spaying. The time required for smaller dog breeds is significantly different than for larger breeds.

While most small dog breeds are neutered/spayed around the six-month mark, this cannot and should not be done with Mastiffs.

Neutering/spaying a Mastiff before the age of one year can have a variety of consequences, including changes in growth patterns. When a male is neutered before his growth plate closes, he may grow taller than he should. This may sound reasonable, but given the Mastiff's size, it will cause a significant joint problem soon.

Between the ages of 18 and 24 months, male Mastiffs should be neutered. At that point, they have nearly reached full size, and neutering will not prevent them from rounding out gracefully. Females should be spayed between the ages of 14 and 18 months to avoid similar complications.

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

Common Questions about American Mastiff

At What Age Is An American Mastiff Fully Grown?

There has been no scientific research conducted to pinpoint the precise age at which Mastiffs stop developing. However, based on my personal experience and that of other Mastiff owners with whom I have spoken, the answer is pretty dynamic.

The critical point to remember is that each Mastiff is unique. Therefore, if your dog falls short of the average expectation, you should not be alarmed.

Unlike several other breeds of dog, Mastiffs often stop developing after about two years. Mastiffs are pretty close to (if not already at) their mature height at two.

Some Mastiff owners will tell you that their dog continued to grow even after reaching the age of two. However, kids are largely filling out and growing into their bodies at that age.

How Long Are American Mastiffs Pregnant?

Dogs typically gestate for roughly 63 days from conception, though this might vary by several days. While this may appear to be a basic response, conception is frequently difficult to determine. Sperm can survive many days inside the female, and eggs can stay viable for up to 48 hours, which means that mating is not a precise indicator of gestation. This makes predicting the duration of pregnancy difficult without the assistance of a veterinarian.

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Hormone measurements provide a significantly more precise estimate of gestational age. Many breeders monitor reproductive hormones during the breeding process via vaginal swabs and blood tests. This enables them to calculate the optimal time to breed their bitch, as well as the gestation period and possible due date.

How Many Puppies Do American Mastiffs Have?

The American Mastiff's litter size is typically between two and five puppies. Because this is a gigantic breed, expect puppies to develop to their full size and outgrow their puppy-like behaviors over two years or more.

What Is The Life Expectancy Of American Mastiffs?

The American Mastiff has a life expectancy of between six and twelve years. Unfortunately, Mastiffs, like all purebred dogs, are predisposed to a variety of inherited health problems, including the following:

  • Entropion
  • Elbow and hip dysplasia
  • Heat sensitivity and heatstroke
  • Heart disease
  • Cancer

Cancer is the greatest cause of mortality in American Mastiffs, according to the Mastiff Club of America4. Lymphoma, osteosarcoma, and mast cell tumors are the most prevalent forms.

While you cannot change your dog's susceptibility to certain diseases such as cancer, you can offer them high-quality veterinary care that can help avoid certain diseases and improve the outcome of diagnosed health problems.

How Much Does It Cost To Own An American Mastiff?

A purebred Mastiff will cost between $1,000 and $3,500, depending on the breeder. When selecting a breeder, get as much information as possible from prior clients and get both parents' thorough medical histories.

It's critical for pet parents to understand that veterinary care can be costly, particularly for emergency procedures or continuous care for chronic disorders. For instance, English Mastiffs are predisposed to cancer, particularly osteosarcoma, a severe bone cancer. Canine osteosarcoma treatment costs can be costly, exceeding $10,000 in rare cases.

How to Determine Whether Your American Mastiff Is Over or Underweight

The easiest way to determine whether your dog is overweight or underweight is to take him/her to a pet nutritionist or veterinarian. They will inform you of the precise percentage of fat on your dog's body. If that appears to be too much stress for you, there are various ways to determine this for yourself at home.

Analyzing your Mastiff's profile is one approach to detect whether they are overweight or underweight. A dog's abdomen is larger than his ribs. A side view of your dog will reveal an inclination between their ribs and waist.

If the incline is excessively high, your dog is likely to be overweight. However, if the inclination is modest or absent entirely, your dog is overweight. The most effective technique to evaluate your Mastiff's profile is to lower yourself to the same level as him and view his body from side to side.

Another method I use is to examine the dog's ribcage. Simply lay both of your thumbs on his spine and spread your palms out across his ribcage.

How To Help Your American Mastiff Lose Weight If He Is Overweight 

If your dog is gaining or losing weight, the best course of action is to take them to a veterinarian to establish the underlying cause. If the reason(s) is/are medical, you will need the help of a veterinarian or pet nutritionist who can advise you and possibly provide a solution. However, if the cause is related to improper feeding and exercise, you may quickly rectify the situation.

If your dog consumes high-calorie foods, you must keep him active to help him burn off excess fat. When the weather is too chilly to exercise outdoors, you might cut his calorie intake to compensate for losing exercise. You just need to know how to balance it out to make sure your dog stays within typical weight.

Conclusion on American Mastiff Growth Chart

Experts would typically urge you to weigh your options before purchasing a large dog. This is because the responsibilities associated with raising a large dog are incomparably more than those associated with raising a little dog. As a result, considerable attention should be given to such a choice.

The Mastiff is one of those breeds that need consideration prior to adoption or purchase. Despite their gigantic size, they require a strong human caregiver. However, they are fundamentally giant cuddly babies trapped in gigantic body.

One technique to care for your Mastiff is to control his weight. Prevent him from becoming overweight or underweight, and give him all the basics necessary to maintain a healthy and happy lifestyle.

Frequently Asked Questions:

Do puppies double in size after six months?

At six months of age, your medium-to-large breed puppy may weigh approximately two-thirds of his adult weight. You can double the weight of a large breed puppy at six months to obtain a sign of how much he will weigh as an adult.

How much food do Mastiffs consume?

The daily suggested amount for an adult Mastiff is normally between 6 and 8 cups of high-quality dry food divided into two meals. More information about feeding your Mastiff may be found in our tips for selecting the proper food, feeding your puppy, and feeding your adult dog.

Are Mastiffs intelligent?

Mastiffs are intelligent and devoted to their owners, but they can be rather stubborn as well. If they are terrified, confused, or their delicate sensibilities are harmed, even by harsh words, it's impossible to get them to do anything.

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