New puppy basics
What size collar does a puppy need?
Last updated 23 September 2026 · How we write and check this
Short answer
Choose a lightweight, adjustable collar that leaves room for two fingers to fit flat between the collar and neck, and plan to size it up several times over the first year as the puppy grows. A basic, inexpensive collar for the first few months makes more sense than an expensive one that will soon be outgrown.
The two finger rule
A collar that is too loose can slip over the head, while one that is too tight restricts breathing and movement. Sliding two fingers flat between the collar and neck is a simple, reliable check most trainers recommend.
Check it weekly during growth spurts
Young puppies can outgrow a collar size within a few weeks during a growth spurt, so checking the fit at least once a week and adjusting or replacing it as needed prevents it from becoming dangerously tight unnoticed.
What to actually check during that weekly test
Beyond the two finger gap, run a finger all the way around the collar looking for red or flattened fur underneath, which signals it has already been too tight for a while rather than just approaching that point. Check this with the puppy standing normally rather than sitting, since a collar can look fine while sitting but feel different once the neck moves during standing or walking.
For a fast growing large or giant breed puppy, budget for resizing or replacing the collar every two to three weeks through the first six months, since some breeds can gain a kilogram or more of body weight in that time, changing neck size noticeably.
A quick release or breakaway style collar is worth considering for a puppy that will wear it indoors as well as out, since a growing puppy exploring furniture and garden fencing has more opportunity to get a fixed buckle collar caught on something than an adult dog with more settled habits.
Key takeaways
- A properly fitted collar allows two fingers to slide flat underneath it.
- Inexpensive, adjustable collars make sense for the first several months of rapid growth.
- Check the fit weekly, since puppies can outgrow a collar size surprisingly fast.