Bullmastiff Puppy Weight Calculator

Calculate the adult weight for your Bullmastiff. Just type your puppy’s current weight and age, and see how big your puppy gets.

Bullmastiff Growth Guide

Breed Overview

The Bullmastiff is a powerful, loyal guardian dog that originated in 19th-century England. Developed by crossing Bulldogs with Mastiffs, the breed was originally used to guard estates and catch poachers. Over time, Bullmastiffs became known not only for their strength and courage but also for their affectionate, calm demeanor with family members.

Classified as a giant breed, Bullmastiffs are known for their imposing size, which makes monitoring their growth especially important. Because of their large frames and rapid early growth, it’s crucial to manage their development with appropriate nutrition and exercise to avoid long-term health issues.

Learn more from the American Kennel Club

Bullmastiff Growth Chart & Weight Ranges

The following growth chart provides average weight ranges for Bullmastiff puppies. Keep in mind that males typically weigh 10–20 lbs more than females at maturity, and individual growth can vary based on genetics, diet, and activity level.

Age	Average Weight (Male)	Average Weight (Female)
4 weeks	10–15 lbs	8–12 lbs
8 weeks	20–30 lbs	18–25 lbs
3 months	35–50 lbs	30–45 lbs
4 months	50–65 lbs	45–60 lbs
6 months	70–90 lbs	65–80 lbs
9 months	90–110 lbs	80–100 lbs
1 year	100–125 lbs	90–110 lbs
18 months	110–135 lbs	100–120 lbs
2 years	115–140 lbs (full grown)	105–125 lbs (full grown)

How Much Bigger Will My Bullmastiff Puppy Get?

Bullmastiff puppies grow rapidly in their first year. Most reach about 50% of their adult weight by 4–5 months old and about 80% by their first birthday. However, giant breeds like Bullmastiffs may continue filling out until 18–24 months of age.

Rule of Thumb:
To estimate adult weight, double your puppy’s weight at 16 weeks. For example, a 50-pound puppy at 4 months might reach 100–120 pounds as an adult.

Be aware that bone growth may be complete by 18 months, but muscle development and chest broadening may continue up to age 2.

Bullmastiff Growth Tips

Nutrition

Bullmastiff puppies should be fed a giant-breed puppy formula to support their bone development without promoting overly rapid growth. Split meals into 3–4 servings per day until 6 months, then reduce to 2 meals per day. Avoid high-calorie, calcium-rich supplements unless recommended by a vet.

Exercise

While regular movement is vital, avoid intense or high-impact activities (like long jogs or stair climbing) before 18 months. Focus on gentle walks and supervised play. Over-exercising a growing puppy can strain joints and soft bones.

Health Watch

Because of their size, Bullmastiffs are prone to hip and elbow dysplasia, panosteitis (growing pains), and joint instability. Regular vet checkups and controlled growth through a balanced diet and exercise can help reduce the risk. Additionally, avoid obesity, as it exacerbates orthopaedic problems.