Puppy feeding and growth
How do I know when my puppy has reached its adult size?
Last updated 23 September 2026 · How we write and check this
Short answer
A dog has typically reached its adult size once weight stays essentially flat across three consecutive monthly weigh ins, and this lines up with the age generally expected for its breed, ranging from around 9 to 12 months for small breeds up to 18 to 24 months for giant breeds.
Weight trend beats appearance
A dog can look fully grown well before it actually is, particularly large and giant breeds that finish gaining height before they finish filling out chest and muscle mass, so relying on how a dog looks rather than tracking its weight over time can lead to switching foods too early.
The three month confirmation rule
Weighing monthly and looking for three consecutive checks with no meaningful change is a reliable, practical way to confirm growth has genuinely stopped rather than just slowed temporarily, which happens periodically even in a puppy that still has real growing left to do.
Cross checking against breed expectations
Compare the age at which weight has flattened against the typical range for the dog's breed or size category. A flat weight at 8 months for a small breed fits the expected timeline, while the same flat weight at 8 months for a giant breed would be unusually early and worth a closer look with a vet.
Key takeaways
- Three consecutive months of stable weight is a reliable sign growth has finished.
- A dog can look fully grown before it has actually finished developing.
- Cross check the age against typical timelines for the breed or size category.
- An unusually early flat weight for a large or giant breed is worth discussing with a vet.