English Mastiff weight chart
English Mastiffs are among the largest dog breeds, with adult males commonly reaching 70 to 100kg or more and females typically somewhat lighter, and their growth follows a genuinely different pattern to smaller dogs — very rapid weight gain in the first year, followed by continued filling out that can carry on for two to three years.
Roughly what to expect by age
Mastiff puppies gain weight remarkably quickly in the first six months, and it is common for a puppy to already weigh 30 to 40kg or more by that point, having started life at only a kilogram or two. By around 12 months, many Mastiffs are approaching 60 to 70kg, though a great deal of individual variation exists depending on sex and genetics.
Unlike a small or medium breed that is largely grown by 12 to 18 months, an English Mastiff typically keeps adding muscle, bone density and overall bulk until somewhere between two and three years old, which is a much longer runway to full maturity than most owners expect from a dog that already looks fully grown much earlier.
Why controlled growth matters so much for this breed
Because giant breeds carry so much weight on a developing skeleton, growing too fast on an overly rich or excessive diet is a recognised risk factor for joint problems later in life, which is why large or giant-breed specific puppy food, fed according to the guidelines and your vet's advice, matters more here than for a small breed puppy.
The goal with a giant breed puppy is steady, controlled growth rather than the fastest possible weight gain, and your vet can help judge whether your Mastiff's growth curve looks appropriate rather than relying on weight figures alone.
When to check in with your vet
If your Mastiff's growth looks noticeably faster or slower than these general figures, or you notice any stiffness, reluctance to move or lameness at any stage of growth, that is worth raising with your vet rather than assuming it will resolve as they mature.
Regular weigh-ins through puppyhood give a much more useful picture of your individual dog's growth trajectory than comparing a single weight against a general chart, and most vets are happy to weigh a growing giant-breed puppy at routine visits without it needing to be a special appointment.
Common questions
- How heavy does an English Mastiff get?
- Adult males commonly reach 70 to 100kg or more, with females typically somewhat lighter. Individual dogs vary considerably, and genetics play a large role in exactly where a particular Mastiff ends up within that range.
- When is an English Mastiff fully grown?
- Much later than most breeds — typically not until somewhere between two and three years old, even though their height and general shape may look close to adult well before that.
- Is it bad for a Mastiff puppy to grow too fast?
- Growing too quickly on an overly rich diet is considered a risk factor for joint problems in giant breeds, which is why steady, controlled growth on an appropriate large-breed puppy food matters, alongside your vet's guidance.
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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.