If you’ve just brought home a Neapolitan Mastiff puppy, the calculator below estimates its adult size from its current weight — personalized to your dog, not just a breed average.
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 Neapolitan Mastiff is a giant breed. Adult males typically weigh 130–155 lb (59.0–70.3 kg) and females 110–130 lb (49.9–59.0 kg). Most Neapolitan Mastiffs 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 Neapolitan Mastiffs stop growing?
Most Neapolitan Mastiffs 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 Neapolitan Mastiff puppy weigh at 4 months?
A typical 4-month-old Neapolitan Mastiff weighs roughly 49–58 lb, about 41% of its adult weight. Use the calculator above with your puppy’s exact weight for a personalized estimate — individual dogs vary.