Mastiff Puppy Weight Calculator

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

Mastiff Breed Profile & Growth Guide

Breed Overview

The Mastiff, also known as the English Mastiff, is one of the oldest and largest dog breeds, dating back thousands of years. Originating in England, these gentle giants were once used as guardians and war dogs but are now cherished for their calm demeanor, loyalty, and protective instincts. Despite their imposing size, Mastiffs are typically affectionate, easygoing, and great with families.

Size Category: Giant
The Mastiff is a giant breed, with adult males often exceeding 160 pounds and females reaching 120 pounds or more. Because of their sheer size and rapid growth, tracking weight and development is crucial. Monitoring growth helps avoid orthopedic issues, overfeeding, and developmental disorders common in large and giant breeds.

Mastiff Growth Chart & Weight Ranges

Age	Male Weight (lbs)	Female Weight (lbs)
4 weeks	5 – 10	4 – 8
8 weeks	18 – 25	15 – 22
3 months	45 – 55	40 – 50
4 months	60 – 75	55 – 70
6 months	90 – 110	80 – 100
9 months	115 – 135	100 – 120
12 months	130 – 160	110 – 140
18 months	150 – 190	125 – 160
24 months	160 – 230	130 – 180

Note: Males are typically larger than females by 20–40 pounds. Adult weight can vary significantly based on genetics, diet, and activity level.

How Much Bigger Will My Mastiff Puppy Get?

Mastiffs are among the slowest-maturing dog breeds due to their giant size. Growth is most rapid in the first year, but they continue to develop well into their second year.

• Most Mastiff puppies reach 50% of their adult weight by 5–6 months.
• Significant weight gain and height increase usually occur between 2 and 12 months.
• Muscle and bone development continues until 18–24 months, or even longer.

Rule of Thumb:
To estimate your Mastiff’s adult size, double its weight at 6 months.

Exception:
Because Mastiffs are giant breeds, they often continue growing until 2.5 years, especially in muscle mass and chest width.

For additional breed-specific care, see the Mastiff Club of America.

Mastiff Growth Nutrition Tips

• Feed a large- or giant-breed puppy formula until at least 18 months to support joint development and prevent overly rapid growth.
• Puppies under 6 months should be fed 3–4 times daily, reducing to 2 meals per day by 6–8 months.
• Avoid overfeeding or excess calcium, which can lead to skeletal issues like panosteitis or hypertrophic osteodystrophy.
• Maintain a lean body condition to reduce stress on developing joints.

Exercise

• Provide moderate, low-impact exercise, such as short walks and gentle play.
• Avoid intense running, jumping, or long stair climbs, especially during the first 18 months.
• Socialization and mental stimulation are essential to help avoid anxiety or overprotectiveness.

Health Watch

• Common growth-related concerns in Mastiffs include:
  • Hip and elbow dysplasia
  • Osteochondritis dissecans (OCD)
  • Panosteitis (growing pains)
  • Entropion (inward-turning eyelids)
• Schedule regular vet checkups and consider early screening for orthopedic conditions via radiographs.
• Support bone health with appropriate calcium/phosphorus ratios and avoid rapid growth spurts.