If you’ve just brought home a Mastiff (English) 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 Mastiff (English) is a giant breed. Adult males typically weigh 160–230 lb (72.6–104.3 kg) and females 120–170 lb (54.4–77.1 kg). Most Mastiff (English)s 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 Mastiff (English)s stop growing?
Most Mastiff (English)s 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 Mastiff (English) puppy weigh at 4 months?
A typical 4-month-old Mastiff (English) weighs roughly 57–81 lb, about 41% of its adult weight. Use the calculator above with your puppy’s exact weight for a personalized estimate — individual dogs vary.