Wondering how big your Bullmastiff puppy will get? Use the calculator below: enter your puppy’s age and current weight to see a personalized growth curve and an adult weight estimate.
Estimates combine your puppy’s current trajectory with typical growth curves for this breed and size class. Individual dogs vary — nutrition, genetics and neuter timing all matter. For health concerns, ask your vet.
The Bullmastiff is a giant breed. Adult males typically weigh 110–130 lb (49.9–59.0 kg) and females 100–120 lb (45.4–54.4 kg). Most Bullmastiffs reach about half their adult weight around 5.0 months, hit 90% by roughly 12.2 months, and are fully grown near 20 months. Giant breeds grow longer than any other dogs — some don’t reach full size until age two.
When do Bullmastiffs stop growing?
Most Bullmastiffs reach their full adult height and weight by about 20 months. Growth is fastest before 5.0 months, then slows steadily — by 12.2 months your puppy will be about 90% of its final size.
How much should a Bullmastiff puppy weigh at 4 months?
A typical 4-month-old Bullmastiff weighs roughly 43–51 lb, about 41% of its adult weight. Use the calculator above with your puppy’s exact weight for a personalized estimate — individual dogs vary.