Bullmastiff weight chart: how to read it
A Bullmastiff is a giant breed, and any weight chart for the breed will show a genuinely wide range — commonly anywhere from around 41kg to 59kg in a fully grown adult — because bone structure and build vary more within giant breeds than within smaller ones. The number on a chart is a reference point, not a target.
Why the range is so wide
Bullmastiffs are a substantial, heavily built breed, and males typically run noticeably heavier than females, so a single chart line rarely fits every dog well. Frame and bone thickness varies between individual dogs too, meaning two Bullmastiffs of the same height at the shoulder can have a meaningfully different healthy weight.
Giant breeds also grow more slowly and for longer than smaller dogs, often not reaching full physical maturity until around 18 months to two years old, so a young adult weighed against an "adult" figure on a chart may simply not be finished growing yet.
Reading body condition alongside the number
A chart tells you a range other Bullmastiffs have fallen into; it does not tell you whether your specific dog is a healthy weight. You should be able to feel the ribs with light pressure without a heavy layer of fat over them, and see a waist tucking in behind the ribs when viewed from above.
If your dog's weight sits outside the typical chart range but their body condition looks and feels right, that is generally more informative than the number alone. If you are ever unsure, your vet can assess body condition properly at a routine check.
Common questions
- How much should an adult Bullmastiff weigh?
- Most adult Bullmastiffs fall somewhere between around 41kg and 59kg, with males typically heavier than females. The wide range reflects genuine variation in frame and build within the breed, so use it as a reference rather than a fixed target.
- At what age is a Bullmastiff fully grown?
- Bullmastiffs are a giant breed and often do not reach full physical maturity until around 18 months to two years old, later than most medium-sized breeds. Weight and frame can both continue developing through that period.
- How do I know if my Bullmastiff is overweight?
- Check body condition rather than relying on a chart figure alone — you should be able to feel their ribs with light pressure and see a waist from above. If neither is the case, it is worth discussing with your vet at their next check-up.
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Written against guidance published by UK veterinary and welfare organisations. Always confirm specifics with your own vet.
Written by Matt Garnett, who runs Giddy Pets and is a lifelong pet owner — not a vet. This is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your animal. How we write these guides.