Mastiff puppies grow toward an adult weight of 160.1–229.9 lb (72.6–104.3 kg) (males) and 119.9–170.0 lb (54.4–77.1 kg) (females) under the American Kennel Club standard; the chart below gives the healthy range at each month, by sex.
Quick answers
- Adults weigh 160.1–229.9 lb (72.6–104.3 kg) (males) and 119.9–170.0 lb (54.4–77.1 kg) (females) under the AKC standard.
- At 6 months a male is usually 107.8–155.0 lb and a female 82.0–116.2 lb — about 67% of adult weight.
- At 12 months a Mastiff is around 92% of its final weight.
- Fully grown at roughly 24 months.
Mastiff weight chart by age
| Age | Male | Female | % of adult |
|---|---|---|---|
| 2 months | 29.5–42.5 lb13.4–19.3 kg | 23.8–33.7 lb10.8–15.3 kg | 19% |
| 3 months | 51.1–73.6 lb23.2–33.4 kg | 40.6–57.3 lb18.4–26.0 kg | 32% |
| 4 months | 71.9–103.2 lb32.6–46.8 kg | 56.0–79.4 lb25.4–36.0 kg | 45% |
| 5 months | 91.5–131.6 lb41.5–59.7 kg | 70.3–99.6 lb31.9–45.2 kg | 57% |
| 6 months | 107.8–155.0 lb48.9–70.3 kg | 82.0–116.2 lb37.2–52.7 kg | 67% |
| 8 months | 132.3–190.0 lb60.0–86.2 kg | 98.8–140.0 lb44.8–63.5 kg | 83% |
| 10 months | 143.5–206.4 lb65.1–93.6 kg | 107.8–152.6 lb48.9–69.2 kg | 90% |
| 12 months | 147.5–211.9 lb66.9–96.1 kg | 109.8–155.6 lb49.8–70.6 kg | 92% |
| 18 months | 156.1–224.2 lb70.8–101.7 kg | 116.6–165.1 lb52.9–74.9 kg | 98% |
| 24 months | 160.1–229.9 lb72.6–104.3 kg | 119.9–170.0 lb54.4–77.1 kg | 100% |
Weigh on the same scale at the same time of day where you can. The trend across several weighings tells you far more than any single row.
Reading the range
The American Kennel Club gives separate ranges for the sexes, 160 to 230 lb for males and 120 to 170 lb for females, and the ranges are wide: 70 lb across for a male.
That width is real, not a hedge. A female Mastiff compared against the male column will read as underweight when she is not, and a male at the top of his range weighs a third more than one at the bottom. Use the column for the dog’s sex and read the trend across weighings rather than any single row.
How a giant breed grows
Mastiffs reach roughly 19% of adult weight at 2 months, about 45% at 4 months, and around 92% at 12 months.
The last stretch is slow: from 12 months to full size takes about as long again as the first year’s final quarter. A Mastiff that looks lanky at 10 months is usually on schedule rather than behind.
Where to go next
- Estimate your own puppyEnter an age and weight to project this breed’s adult size.
- Compare across giant breedsThe same curve applied to every giant breed on the site.
- Puppy growth chart by ageAll five size classes in one table, and what the ranges mean.
- Body condition scoreThe 9-point scale vets use, and why it beats the scale alone.
Other giant breeds
Frequently asked questions
What is the average weight of a Mastiff?
An adult male Mastiff weighs 160.1–229.9 lb (72.6–104.3 kg) and an adult female 119.9–170.0 lb (54.4–77.1 kg), according to the American Kennel Club breed standard.
How much should a 3 month old Mastiff weigh?
A male is typically 51.1–73.6 lb (23.2–33.4 kg) and a female 40.6–57.3 lb (18.4–26.0 kg) — around 32% of adult weight.
How much should a 4 month old Mastiff weigh?
Roughly 71.9–103.2 lb for a male and 56.0–79.4 lb for a female, about 45% of the way to adult weight.
How much does a 6 month old Mastiff weigh?
A male is usually 107.8–155.0 lb (48.9–70.3 kg) and a female 82.0–116.2 lb (37.2–52.7 kg).
How much does a 12 month old Mastiff weigh?
147.5–211.9 lb for males and 109.8–155.6 lb for females — about 92% of final weight, with the rest filling in over the following months.
How big will my Mastiff get?
At 45% of adult weight by 4 months, a rough shortcut is to double a four-month weight. The calculator on the home page does this properly, using the growth curve for this size class and returning a range rather than one number.
When is a Mastiff fully grown?
Height is usually settled first; weight keeps filling in until around 24 months. The last 8% of adult weight takes roughly as long as the jump from 3 to 4 months.
Do male and female Mastiffs weigh different amounts?
Yes, and by enough to matter. Adult males run 160.1–229.9 lb (72.6–104.3 kg) against 119.9–170.0 lb (54.4–77.1 kg) for females. Comparing a female against a chart that does not separate the sexes will usually make her look underweight when she is not.
What size class is a Mastiff?
A giant breed, defined by adult weight. That classification determines the growth curve used here: veterinary research shows dogs of similar adult size grow at similar rates regardless of breed.
Is my Mastiff puppy underweight if it is below the chart?
Not necessarily. The table shows the middle of the healthy range, so plenty of healthy puppies sit below it. A puppy that is consistently below and not gaining, or that has dropped from a higher line to a lower one, is worth a vet visit. A single reading below the range is not.
How can I tell if my Mastiff is a healthy weight?
Body condition tells you more than the scale. You should be able to feel the ribs under a thin layer of fat without pressing, see a waist from above, and see the belly tuck up from the side. A dog can sit inside the weight range and still carry too much fat.
Why do Mastiff growth charts disagree with each other?
Most published charts come from one breeder’s litters or from unsourced rules of thumb, and many do not say whether the figures are for males, females or both. The ranges here come from centile curves fitted to millions of veterinary bodyweight records, scaled to the AKC adult range, and split by sex.
Does neutering change how much a Mastiff weighs?
The research behind these curves found neutering shifted growth trajectory only slightly, by less than the variation between individual dogs, so separate curves were not needed. Neutering is associated with a higher chance of becoming overweight in adulthood, which is a body condition question rather than a growth chart one.
Where these numbers come from
Adult weights are the breed standard figures published by the American Kennel Club. The month-by-month ranges are estimates rather than measurements of this breed: they come from growth centile curves built from around 15 million bodyweight records collected at US primary-care veterinary hospitals, published open-access by Salt and colleagues, and scaled to the adult range above. That research found dogs of similar adult size grow at similar rates regardless of breed, which is what makes the scaling valid. The records were collected between 1994 and 2013 and describe dogs attending veterinary clinics rather than an idealised population. The derived table, the filtering steps and the known gaps are all published, so the arithmetic here can be checked rather than taken on trust.
- American Kennel Club — Mastiff breed standard
- Mastiff Club of America — the AKC parent club for the breed
- Salt C, Morris PJ, Wilson D, Lund EM, German AJ (2017). Growth standard charts for monitoring bodyweight in dogs of different sizes. PLoS ONE 12(9): e0182064
- Supporting dataset, University of Liverpool DataCat (CC BY 4.0)